Sulfonium compound, chemically amplified resist composition, and patterning process

ABSTRACT

A novel sulfonium compound of formula (A) and a chemically amplified resist composition comprising the same as a PAG are provided. When processed by photolithography using KrF or ArF excimer laser, EB or EUV, the resist composition has a high sensitivity and reduced acid diffusion and is improved in lithography properties.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2019-072757 filed in Japan on Apr. 5,2019, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a sulfonium compound, a chemically amplifiedresist composition, and a patterning process.

BACKGROUND ART

While a number of recent efforts are being made to achieve a finerpattern rule in the drive for higher integration and operating speeds inLSIs, DUV and EUV lithography processes are thought to hold particularpromise as the next generation in microfabrication technology. Inparticular, photolithography using an ArF excimer laser is requisite tothe micropatterning technique capable of achieving a feature size of0.13 μm or less.

The ArF lithography started partial use from the fabrication of 130-nmnode devices and became the main lithography since 90-nm node devices.Although lithography using F₂ laser (wavelength 157 nm) was initiallythought promising as the next lithography for 45-nm node devices, itsdevelopment was retarded by several problems. A highlight was suddenlyplaced on the ArF immersion lithography that introduces a liquid havinga higher refractive index than air (e.g., water, ethylene glycol,glycerol) between the projection lens and the wafer, allowing theprojection lens to be designed to a numerical aperture (NA) of 1.0 orhigher and achieving a higher resolution. See Non-Patent Document 1. TheArF immersion lithography is now implemented on the commercial stage.The immersion lithography requires a resist material which issubstantially insoluble in water.

In the photolithography using an ArF excimer laser (wavelength 193 nm),a high sensitivity resist material capable of achieving a highresolution at a small dose of exposure is needed to prevent thedegradation of precise and expensive optical system materials. Amongseveral measures for providing high sensitivity resist material, themost common is to select each component which is highly transparent atthe wavelength of 193 nm. For example, polymers of acrylic acid andderivatives thereof, norbornene-maleic anhydride alternating copolymers,polynorbomene, ring-opening metathesis polymerization (ROMP) polymers,and hydrogenated ROMP polymers have been proposed as the base resin.This choice is effective to some extent in that the transparency of aresin alone is increased.

Recently a highlight is put on the negative tone resist adapted fororganic solvent development as well as the positive tone resist adaptedfor alkaline development. It would be desirable if a very fine holepattern, which is not achievable with the positive tone, is resolvablethrough negative tone exposure. To this end, a positive resist materialfeaturing a high resolution is subjected to organic solvent developmentto form a negative pattern. An attempt to double a resolution bycombining two developments, alkali development and organic solventdevelopment is under study. As the ArF resist material for negative tonedevelopment with organic solvent, positive ArF resist compositions ofthe prior art design may be used. Such pattern forming processes aredescribed in Patent Documents 1 to 3.

To meet the current rapid progress of microfabrication technology,development efforts are put on not only the process, but also the resistmaterial. Studies have also been made on photoacid generators (PAGs).Commonly used are sulfonium salts of triphenylsulfonium cation withperfluoroalkanesulfonic acid anion. These salts generateperfluoroalkanesulfonic acids, especially perfluorooctanesulfonic acid(PFOS), which are considered problematic with respect to theirnon-degradability, biological concentration and toxicity. It is ratherrestricted to apply these salts to the resist material. Instead, PAGscapable of generating perfluorobutanesulfonic acid are currently used,but are awkward to achieve a high resolution because of substantialdiffusion of the generated acid in the resist material. To address theproblem, partially fluorinated alkane sulfonic acids and salts thereofare developed. For instance, Patent Document 1 describes the prior artPAGs capable of generating α,α-difluoroalkanesulfonic acid, such asdi(4-tert-butylphenyl)iodonium1,1-difluoro-2-(1-naphthyl)ethanesulfonate and PAGs capable ofgenerating α,α,β,β-tetrafluoroalkanesulfonic acid. Despite a reduceddegree of fluorine substitution, these PAGs still have the followingproblems. Since they do not have a decomposable substituent group suchas ester structure, they are unsatisfactory from the aspect ofenvironmental safety or ease of decomposition. The molecular design tochange the size of alkanesulfonic acid is limited. Fluorine-containingstarting reactants are expensive.

As the circuit line width is reduced, the degradation of contrast byacid diffusion becomes more serious for the resist material. The reasonis that the pattern feature size is approaching the diffusion length ofacid. This invites a lowering of mask fidelity and a degradation ofpattern rectangularity because a dimensional shift on wafer (known asmask error factor (MEF)) relative to a dimensional shift on mask isexaggerated. Accordingly, to gain more benefits from a reduction ofexposure light wavelength and an increase of lens NA, the resistmaterial is required to increase a dissolution contrast or restrain aciddiffusion, as compared with the prior art materials. One approach is tolower the bake temperature for suppressing acid diffusion and hence,improving MEF. A low bake temperature, however, inevitably leads to alow sensitivity.

Incorporating a bulky substituent or polar group into PAG is effectivefor suppressing acid diffusion. Patent Document 4 discloses a PAGcapable of generating 2-acyloxy-1,1,3,3,3-pentafluoropropane-1-sulfonicacid which is fully soluble and stable in resist solvents and allows fora wide span of molecular design. In particular, a PAG having a bulkysubstituent incorporated therein or capable of generating2-(1-adamantyloxy)-1,1,3,3,3-pentafluoropropane-1-sulfonic acid ischaracterized by slow acid diffusion. Patent Documents 5 to 7 describePAGs having fused ring lactone, sultone or thiolactone incorporated asthe polar group. Although some improvement in performance is observeddue to the acid diffusion suppressing effect of the polar groupincorporated, they are still insufficient in precise control of aciddiffusion. Their lithography performance is unsatisfactory whenevaluated totally in terms of MEF, pattern profile and sensitivity.

Patent Documents 8 to 14 describe PAGs of betaine structure possessingcation and anion moieties in a common molecule. After exposure, an acidis generated, and the cation moiety is decomposed at the same time.Since the generated acid which is attached to the anion moiety is notsubstantially reduced in molecular weight, acid diffusion is controlled.However, the PAGs themselves are little soluble in the resist solventand developer, raising such problems as precipitation during shelfstorage and defect formation after development. Although these PAGs areeffective for improving performance to some extent, they are stillinsufficient in sensitivity and precise control of acid diffusion. Thereis the desire to have a PAG capable of meeting a high sensitivity, lowacid diffusion, and solvent solubility.

CITATION LIST

-   Patent Document 1: JP-A 2008-281974-   Patent Document 2: JP-A 2008-281975-   Patent Document 3: JP 4554665-   Patent Document 4: JP-A 2007-145797-   Patent Document 5: JP 5061484-   Patent Document 6: JP-A 2016-147879-   Patent Document 7: JP-A 2015-063472-   Patent Document 8: JP 5317181-   Patent Document 9: JP 5723802-   Patent Document 10: JP 5865725-   Patent Document 11: JP 6130109-   Patent Document 12: JP 6155013-   Patent Document 13: JP-A 2013-008020-   Patent Document 14: JP-A 2018-043977-   Non-Patent Document 1: Journal of Photopolymer Science and    Technology, Vol. 17, No. 4, p 587 (2004)

DISCLOSURE OF INVENTION

While it is recently demanded to form resist patterns at a highresolution, a resist composition using a conventional PAG fails to fullysuppress acid diffusion. As a result, lithography performance factorssuch as contrast, MEF and LWR are degraded.

An object of the invention is to provide a novel sulfonium compound anda chemically amplified resist composition comprising the same as aphotoacid generator, the resist composition, when processed byphotolithography using high-energy radiation such as KrF or ArF excimerlaser, EB or EUV as the energy source, exhibiting a high sensitivity andreduced acid diffusion and being improved in EL, MEF, and LWR; and apattern forming process using the resist composition.

The inventors have found that a chemically amplified resist compositioncomprising a sulfonium compound of specific structure as a photoacidgenerator has a high sensitivity, is reduced in acid diffusion, improvedin many lithography performance factors including EL, MEF, and LWR, andthus best suited for precise micropatterning.

In one aspect, the invention provides a sulfonium compound having theformula (A).

Herein Q¹ and Q² are each independently fluorine or a C₁-C₆ fluoroalkylgroup. Q³ and Q⁴ are each independently hydrogen, fluorine or a C₁-C₆fluoroalkyl group, a is an integer of 1 to 4, b is 1 or 2, and c is aninteger of 0 to 3. L^(a1) to L^(a4) are each independently a singlebond, ether bond, ester bond, sulfonic acid ester bond, carbonate bondor carbamate bond. X^(L1) and X^(L2) are each independently a singlebond or a C₂-C₄₀ divalent hydrocarbon group which may contain aheteroatom. R^(a) is hydrogen or a C₁-C₂₀ monovalent hydrocarbon groupwhich may contain a heteroatom. R^(b) and R^(c) are each independently aC₂-C₄₀ monovalent hydrocarbon group which may contain a heteroatom,R^(b) and R^(c) may bond together to form a ring with the oxygen atomsto which they are attached and the intervening carbon atom. R¹ is aC₁-C₅₀ (a+1)-valent hydrocarbon group which may contain a heteroatom. R²is a C₁-C₅₀ monovalent hydrocarbon group which may contain a heteroatom.R³ is a C₁-C₅₀ divalent hydrocarbon group which may contain aheteroatom. In the case of b=1, R¹ and R², or R² and R³ may bondtogether to form a ring with the sulfur atom to which they are attached.In the case of b=2, R¹ and R³, or two R¹ may bond together to form aring with the sulfur atom to which they are attached.

Preferably the sulfonium compound has the formula (A-1).

Herein Q¹ to Q⁴, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a), R^(b), R^(c),R², R³, a, b and c are as defined above, R^(d) is a C₁-C₂₀ monovalenthydrocarbon group which may contain a heteroatom, d is an integer of 0to 4, the sum a+d is 1 to 5, in the case of d≥2, each R^(d) may be thesame or different, and two R^(d) may bond together to form a ring withthe atoms to which they are attached.

More preferably the sulfonium compound has the formula (A-2).

Herein Q¹ to Q⁴, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a) to R^(d), a, b,c and d are as defined above, R^(e) and R^(f) are each independently aC₁-C₂₀ monovalent hydrocarbon group which may contain a heteroatom, e isan integer of 0 to 5, f is an integer of 0 to 4, in the case of e≥2,each R^(e) may be the same or different, and two R^(e) may bond togetherto form a ring with the atoms to which they are attached, and in thecase of f≥2, each R^(f) may be the same or different, and two R^(f) maybond together to form a ring with the atoms to which they are attached.

Even more preferably the sulfonium compound has the formula (A-3).

Herein Q¹ to Q³, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a) to R^(f), a, b,d, e and f are as defined above.

Also provided is a photoacid generator comprising the sulfonium compounddefined above.

In another aspect, the invention provides a chemically amplified resistcomposition comprising the photoacid generator defined above and a baseresin comprising recurring units having the formula (a1) or (a2).

Herein R^(A) is each independently hydrogen, fluorine, methyl ortrifluoromethyl, Z^(A) is a single bond, phenylene, naphthylene or(backbone)-C(═O)—O—Z^(A1)—, Z^(A1) is a C₁-C₁₀ alkanediyl group whichmay contain a hydroxyl moiety, ether bond, ester bond or lactone ring,or phenylene or naphthylene, Z^(B) is a single bond or(backbone)-C(═O)—O—, X^(A) and X^(B) are each independently an acidlabile group, R¹¹ is a C₁-C₂₀ monovalent hydrocarbon group which maycontain a heteroatom, and n is an integer of 0 to 4.

In a preferred embodiment, the base resin further comprises recurringunits having the formula (b1) or (b2).

Herein R^(A) is each independently hydrogen, fluorine, methyl ortrifluoromethyl, Y^(A) is hydrogen or a polar group containing at leastone structure selected from the group consisting of hydroxyl, cyano,carbonyl, carboxyl, ether bond, ester bond, sulfonic acid ester bond,carbonate bond, lactone ring, sultone ring and carboxylic anhydride, andm is 1 or 2.

In a preferred embodiment, the base resin further comprises recurringunits of at least one type selected from recurring units having theformulae (c1) to (c3).

Herein R^(A) is each independently hydrogen, fluorine, methyl ortrifluoromethyl. Z¹ is a single bond, phenylene, —O—Z¹¹—, —C(═O)—O—Z¹¹—or —C(═O)—NH—Z¹¹—, wherein Z¹¹ is a C₁-C₂₀ alkanediyl group, C₂-C₂₀alkenediyl group or phenylene group, which may contain a carbonylmoiety, ester bond, ether bond or hydroxyl moiety. Z² is a single bondor —Z²¹—C(═O)—O—, wherein Z²¹ is a C₁-C₂₀ divalent hydrocarbon groupwhich may contain a heteroatom. Z³ is a single bond, methylene,ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, —C(═O)—O—Z³¹— or—C(═O)—NH—Z³¹—, wherein Z³¹ is a C₁-C₆ alkanediyl group, C₂-C₆alkenediyl group or phenylene group, which may contain a carbonylmoiety, ester bond, ether bond or hydroxyl moiety. R²¹ and R²² are eachindependently a C₁-C₂₀ monovalent hydrocarbon group which may contain aheteroatom, R²¹ and R²² may bond together to form a ring with the sulfuratom to which they are attached. M⁻ is a non-nucleophilic counter ion.A⁺ is an ammonium, sulfonium or iodonium cation.

The resist composition may further comprise an organic solvent.

The resist composition may further comprise a photoacid generator otherthan the photoacid generator defined above.

Preferably, the other photoacid generator has the formula (1) or (2).

Herein R¹⁰¹, R¹⁰² and R¹⁰³ are each independently a C₁-C₂₀ monovalenthydrocarbon group which may contain a heteroatom, any two of R¹⁰¹, R¹⁰²and R¹⁰³ may bond together to form a ring with the sulfur atom to whichthey are attached, and X⁻ is an anion selected from the followingformulae (1A) to (1D):

wherein R^(fa), R^(fb1), R^(fb2), R^(fc1), R^(fc2) and R^(fc3) are eachindependently fluorine or a C₁-C₄₀ monovalent hydrocarbon group whichmay contain a heteroatom, or a pair of R^(fb1) and R^(fb2), or R^(fc1)and R^(fc2) may bond together to form a ring with the carbon atom towhich they are attached and any intervening atoms, R^(fd) is a C₁-C₄₀monovalent hydrocarbon group which may contain a heteroatom,

wherein R²⁰¹ and R²⁰² are each independently a C₁-C₃₀ monovalenthydrocarbon group which may contain a heteroatom, R²⁰³ is a C₁-C₃₀divalent hydrocarbon group which may contain a heteroatom, any two ofR²⁰¹, R²⁰² and R²⁰³ may bond together to form a ring with the sulfuratom to which they are attached, L^(A) is a single bond, ether bond or aC₁-C₂₀ divalent hydrocarbon group which may contain a heteroatom, X^(a),X^(b), X^(c) and X^(d) are each independently hydrogen, fluorine ortrifluoromethyl, at least one of X^(a), X^(b), X^(c) and X^(d) beingfluorine or trifluoromethyl.

The resist composition may further comprise a compound having theformula (3) or (4).R^(q1)—SO₃ ⁻Mq⁺  (3)R^(q2)—CO₂ ⁻Mq⁺  (4)Herein R^(q1) is hydrogen or a C₁-C₄₀ monovalent hydrocarbon group whichmay contain a heteroatom, exclusive of the group wherein hydrogen bondedto the carbon atom at α-position relative to the sulfo group issubstituted by fluorine or fluoroalkyl, R^(q2) is hydrogen or a C₁-C₄₀monovalent hydrocarbon group which may contain a heteroatom, and Mq⁺ isan onium cation.

The resist composition may further comprise an amine compound.

The resist composition may further comprise a surfactant which isinsoluble or substantially insoluble in water and soluble in alkalinedeveloper, and/or a surfactant which is insoluble or substantiallyinsoluble in water and alkaline developer.

In a further aspect, the invention provides a pattern forming processcomprising the steps of applying the chemically amplified resistcomposition defined above to form a resist film on a substrate, exposinga selected region of the resist film to KrF excimer laser, ArF excimerlaser, EB or EUV, and developing the exposed resist film in a developer.

In a preferred embodiment, the developing step uses an alkaline aqueoussolution as the developer, thereby forming a positive pattern in whichan exposed region of the resist film is dissolved away and an unexposedregion of the resist film is not dissolved.

In another preferred embodiment, the developing step uses an organicsolvent as the developer, thereby forming a negative pattern in which anunexposed region of the resist film is dissolved away and an exposedregion of the resist film is not dissolved.

The organic solvent is typically selected from among 2-octanone,2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone,3-hexanone, diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate,butyl formate, isobutyl formate, pentyl formate, isopentyl formate,methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate,benzyl acetate, methyl phenylacetate, benzyl formate, phenylethylformate, methyl 3-phenylpropionate, benzyl propionate, ethylphenylacetate, and 2-phenylethyl acetate.

In a preferred embodiment, the exposure step is carried out by immersionlithography while a liquid having a refractive index of at least 1.0 isheld between the resist film and a projection lens.

In a preferred embodiment, a protective film is formed on the resistfilm prior to the exposure step, and immersion lithography is carriedout while the liquid is held between the protective film and theprojection lens.

Advantageous Effects of Invention

The inventive sulfonium compound is useful as a PAG in a chemicallyamplified resist composition. When the chemically amplified resistcomposition comprising the inventive sulfonium compound is processed byphotolithography, a resist pattern with improved EL, MEF, and LWR isformed, because the extent of acid diffusion is significantlycontrolled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the ¹H-NMR spectrum of PAG-1 in Example1-1-6.

FIG. 2 is a diagram showing the ¹H-NMR spectrum of PAG-2 in Example 1-2.

FIG. 3 is a diagram showing the ¹H-NMR spectrum of PAG-4 in Example 1-4.

FIG. 4 is a diagram showing the ¹H-NMR spectrum of PAG-5 in Example1-5-3.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. “Optional” or“optionally” means that the subsequently described event orcircumstances may or may not occur, and that description includesinstances where the event or circumstance occurs and instances where itdoes not. The notation (Cn-Cm) means a group containing from n to mcarbon atoms per group. In chemical formulae, Me stands for methyl, Acfor acetyl, and the broken line designates a valence bond.

The abbreviations and acronyms have the following meaning.

EB: electron beam

EUV: extreme ultraviolet

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

EL: exposure latitude

LWR: line width roughness

MEF: mask error factor

CDU: critical dimension uniformity

DOF: depth of focus

Sulfonium Compound

The invention provides a sulfonium compound having the formula (A).

In formula (A), Q¹ and Q² are each independently fluorine or a C₁-C₆fluoroalkyl group. Q³ and Q⁴ are each independently hydrogen, fluorineor a C₁-C₆ fluoroalkyl group.

In formula (A), a is an integer of 1 to 4, preferably 1; b is 1 or 2; cis an integer of 0 to 3, preferably 1.

In formula (A), L^(a1) to L^(a4) are each independently a single bond,ether bond, ester bond, sulfonic acid ester bond, carbonate bond orcarbamate bond. Preferably, L^(a1) is a single bond, ether bond or esterbond, more preferably a single bond; L^(a2) is a single bond, ether bondor ester bond, more preferably an ether bond; L^(a3) is a single bond,ether bond or ester bond, more preferably a single bond; and L^(a4) is asingle bond, ether bond or ester bond, more preferably a single bond.

In formula (A), X^(L1) and X^(L2) are each independently a single bondor a C₂-C₄₀ divalent hydrocarbon group which may contain a heteroatom.The divalent hydrocarbon group may be straight, branched or cyclic andexamples thereof include alkanediyl groups and divalent saturated cyclichydrocarbon groups. Typical of the heteroatom are oxygen, nitrogen andsulfur. Preferably X^(L1) and X^(L2) each are a single bond.

Preferred examples of the C₂-C₄₀ divalent hydrocarbon group representedby X^(L1) and X^(L2) are shown below. In the following formulae, * atone end designates a bond to L^(a1) or L^(a2), and L^(a3) or L^(a4).

Of these, structures X^(L)-1 to X^(L)-22 and X^(L)-47 to X^(L)-49 arepreferred, with structures X^(L)-1 to X^(L)-17 being more preferred.

In formula (A), R^(a) is hydrogen or a C₁-C₂₀ monovalent hydrocarbongroup which may contain a heteroatom. The monovalent hydrocarbon groupmay be straight, branched or cyclic. Examples include alkyl groups suchas methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,tert-pentyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl,cyclohexyl, 2-ethylhexyl, cyclopentylmethyl, cyclopentylethyl,cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl,norbomyl, tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl, andadamantylmethyl, and aryl groups such as phenyl, naphthyl andanthracenyl. In the monovalent hydrocarbon group, some hydrogen may besubstituted by a moiety containing a heteroatom such as oxygen, sulfur,nitrogen or halogen, or a moiety containing a heteroatom such as oxygen,sulfur or nitrogen may intervene between carbon atoms, so that the groupmay contain a hydroxyl, cyano, carbonyl, ether bond, ester bond,sulfonic acid ester bond, carbonate bond, carbamate bond, amide bond,imide bond, lactone ring, sultone ring, thiolactone ring, lactam ring,sultam ring, carboxylic anhydride (—C(═O)—O—C(═O)—), or haloalkylmoiety. Inter alia, R^(a) is preferably hydrogen, C₁-C₆ alkyl or C₆-C₁₀aryl, more preferably hydrogen or methyl, most preferably methyl.

In formula (A), R^(b) and R^(c) are each independently a C₂-C₄₀monovalent hydrocarbon group which may contain a heteroatom, R^(b) andR^(c) may bond together to form a ring with the oxygen atoms to whichthey are attached and the intervening carbon atom. The monovalenthydrocarbon group may be straight, branched or cyclic and examplesthereof are as exemplified above for R^(a). When some hydrogen in themonovalent hydrocarbon group is substituted by halogen, fluorinesubstitution is preferred.

Where R^(b) and R^(c) do not bond together to form a ring structure,each forms an acyclic acetal structure with the adjacent oxygen atom.Where R^(b) and R^(c) bond together to forma ring, they forma cyclicacetal structure with the adjacent oxygen atoms. Of these cases, theformation of a cyclic acetal structure is preferred in view of thestability of acetal structure. Of the cyclic acetal structures, 5-, 6-and 7-membered ring acetal structures are more preferred.

Examples of the acyclic or cyclic acetal structure are shown below, butnot limited thereto. Herein R^(a) is as defined above, and the brokenline designates a valence bond to L^(a3).

In formula (A), R¹ is a C₁-C₅₀ (a+1)-valent hydrocarbon group which maycontain a heteroatom, preferably of C₁-C₂₀.

The hydrocarbon group R¹ may be straight, branched or cyclic, andaliphatic or aromatic. Exemplary, non-limiting structures are shownbelow. In the formulae, the broken line designates a valence bond to S⁺or L^(a4).

R¹ is preferably an aromatic hydrocarbon group, more preferably a groupderived from benzene or naphthalene, most preferably a group derivedfrom benzene.

In formula (A), R² is a C₁-C₅₀ monovalent hydrocarbon group which maycontain a heteroatom, preferably of C₁-C₂₀. The monovalent hydrocarbongroup maybe straight, branched or cyclic. Examples thereof includemonovalent aliphatic hydrocarbon groups such as alkyl and alkenyl groupsand monovalent aromatic hydrocarbon groups such as aryl and aralkylgroups.

Suitable alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl,cyclohexyl, cycloheptyl, cyclopropylmethyl, 4-methylcyclohexyl,cyclohexylmethyl, norbornyl, and adamantyl. Suitable alkenyl groupsinclude vinyl, allyl, propenyl, butenyl, hexenyl and cyclohexenyl.

Suitable aryl groups include phenyl; alkylphenyl groups such as2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl,4-tert-butylphenyl, 4-n-butylphenyl, and 2,4-dimethylphenyl; naphthyl;alkylnaphthyl groups such as methylnaphthyl and ethylnaphthyl; anddialkylnaphthyl groups such as dimethylnaphthyl and diethylnaphthyl.Suitable aralkyl groups include benzyl, 1-phenylethyl and 2-phenylethyl.

In these hydrocarbon groups, some hydrogen may be substituted by amoiety containing a heteroatom such as oxygen, sulfur, nitrogen orhalogen, or some carbon may be replaced by a moiety containing aheteroatom such as oxygen, sulfur or nitrogen, so that the group maycontain a hydroxyl, cyano, carbonyl, ether bond, ester bond, sulfonicacid ester bond, carbonate bond, lactone ring, sultone ring, carboxylicanhydride, or haloalkyl moiety.

Examples of the heteroatom-containing monovalent aliphatic hydrocarbongroup include oxo-containing alkyl groups such as 2-oxocyclopentyl,2-oxocyclohexyl, 2-oxopropyl, 2-oxoethyl, 2-cyclopentyl-2-oxoethyl,2-cyclohexyl-2-oxoethyl, and 2-(4-methylcyclohexyl)-2-oxoethyl. Examplesof the heteroatom-containing monovalent aromatic hydrocarbon groupinclude heteroaryl groups such as thienyl; hydroxyphenyl groups such as4-hydroxyphenyl; fluorinated phenyl groups such as fluorophenyl anddifluorophenyl; alkoxyphenyl groups such as 4-methoxyphenyl,3-methoxyphenyl, 2-methoxyphenyl, 4-ethoxyphenyl, 4-tert-butoxyphenyl,and 3-tert-butoxyphenyl; alkoxynaphthyl groups such as methoxynaphthyl,ethoxynaphthyl, n-propoxynaphthyl, and n-butoxynaphthyl;dialkoxynaphthyl groups such as dimethoxynaphthyl and diethoxynaphthyl;and aryloxoalkyl groups such as 2-phenyl-2-oxoethyl,2-(1-naphthyl)-2-oxoethyl, and 2-(2-naphthyl)-2-oxoethyl.

Of these, R² is preferably a monovalent aromatic hydrocarbon group whichmay contain a heteroatom, more preferably an aryl group which maycontain a heteroatom, and even more preferably phenyl, alkylphenyl orfluorinated phenyl.

In formula (A), R³ is a C₁-C₅₀ divalent hydrocarbon group which maycontain a heteroatom, preferably of C₁-C₂₀. The divalent hydrocarbongroup maybe straight, branched or cyclic. Examples thereof includestraight alkanediyl groups such as methylene, ethylene,propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl,heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl,undecane-1,11-diyl, dodecane-1,12-diyl, tridecane-1,13-diyl,tetradecane-1,14-diyl, pentadecane-1,15-diyl, hexadecane-1,16-diyl,heptadecane-1,17-diyl; divalent saturated cyclic hydrocarbon groups suchas cyclopentanediyl, cyclohexanediyl, norbornanediyl, andadamantanediyl; and divalent aromatic hydrocarbon groups such asphenylene and naphthylene. Also included are the foregoing groups inwhich some hydrogen is substituted by an alkyl group such as methyl,ethyl, propyl, n-butyl or tert-butyl, or in which some hydrogen issubstituted by a moiety containing a heteroatom such as oxygen, sulfur,nitrogen or halogen, so that the group may contain a hydroxyl, cyano,carbonyl, ether bond, ester bond, sulfonic acid ester bond, carbonatebond, lactone ring, sultone ring, carboxylic anhydride or haloalkylmoiety. Of these, R³ is preferably a divalent aromatic hydrocarbongroup, more preferably phenylene or a phenylene group substituted withan alkyl moiety or heteroatom-containing moiety.

In formula (A), any two of R¹, R² and R³ may bond together to form aring with the sulfur atom to which they are attached. Examples of thesulfonium cation moiety in this embodiment include the following.

Of the sulfonium compounds having formula (A), those compounds havingthe formula (A-1) are preferred.

Herein Q¹ to Q⁴, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a), R^(b), R^(c),R², R³, a, b and c are as defined above. R^(d) is a C₁-C₂₀ monovalenthydrocarbon group which may contain a heteroatom, d is an integer of 0to 4, and the sum a+d is 1 to 5. In the case of d≥2, each R^(d) may bethe same or different, and two R^(d) may bond together to form a ringwith the atoms to which they are attached.

Of the sulfonium compounds having formula (A-1), those compounds havingthe formula (A-2) are more preferred.

Herein Q¹ to Q⁴, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a) to R^(d), a, b,c and d are as defined above. R^(e) and R^(f) are each independently aC₁-C₂₀ monovalent hydrocarbon group which may contain a heteroatom, e isan integer of 0 to 5, and f is an integer of 0 to 4. In the case of e≥2,each R^(e) may be the same or different, and two R^(e) may bond togetherto form a ring with the atoms to which they are attached. In the case off≥2, each R^(f) may be the same or different, and two R^(f) may bondtogether to form a ring with the atoms to which they are attached.

Of the sulfonium compounds having formula (A-2), those compounds havingthe formula (A-3) are preferred.

Herein Q¹ to Q³, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a) to R^(f), a, b,d, e and f are as defined above.

Examples of the sulfonium compound having formula (A) are shown below,but not limited thereto. Herein Q³ is as defined above.

The inventive sulfonium compound is a useful PAG. The sulfonium compoundis structurally characterized by a betaine structure possessing cationand anion moieties within a common molecule, and an acetal structure inthe molecule. After an acid is generated upon exposure, a salt compoundis formed between molecules and when another PAG is co-present, a saltcompound is formed between the acid and the other PAG, probably assumingan apparently giant compound. After the acid generation, not onlydecomposition of the cation moiety, but also acid-catalyzed deprotectionreaction of the acetal structure takes place. It is presumed that theacetal structure converts to a ketone (or aldehyde) structure which is apolar group, whereby the dissolution contrast increases.

For the same reason, the behavior that acid diffusion is suppressed ispresumed. This leads to improvements in EL, MEF and LWR as well as DOFand CDU. Heretofore, DOF and CDU are in a tradeoff relationship as aresult of scramble for resolution performance or acid diffusion control.By contrast, the inventive resist composition is successful in improvingboth the factors at the same time, and thus useful. The conversion ofthe acetal structure to a polar ketone (or aldehyde) structure ensuresthat in the positive tone alkaline development process, the affinity toalkaline developer is improved and development defectivity in theexposed region is reduced. Inversely in the negative tone organicsolvent development process, the solubility in the organic solventlowers, and percent film retention in the exposed region is improved.

The inventive sulfonium compound may be prepared according to the schemeshown below. Although reference is made to the synthesis of a sulfoniumcompound of cyclic acetal structure having formula (A-a), the synthesismethod is not limited thereto.

Herein R^(d), R^(e), R^(f), Q¹ to Q⁴, c, d, e and f are as definedabove, X is a halogen atom, X⁻ is a halide ion, and M⁺ is a countercation.

In the first step, coupling reaction is performed between Reactant A andReactant B to form Intermediate A, diaryl sulfide. Reactants A and B areavailable as commercial products or can be synthesized by a standardmethod.

The reaction may be performed by a well-known organic synthesis method,specifically by dissolving Reactants A and B in a solvent such asN-methylpyrrolidone, dimethylformamide or dimethylacetamide, and addinga copper catalyst and a base to the solution. Examples of the coppercatalyst used herein include copper(I) iodide, copper(I) bromide, andcopper(I) chloride. Examples of the base used herein include organicbases such as triethylamine, pyridine and diisopropylethylamine andinorganic bases such as sodium hydroxide, potassium carbonate andlithium hydroxide. The reaction temperature may be from 80° C. to aboutthe boiling point of the solvent. It is desirable from the standpoint ofyield that the reaction time is determined so as to drive the reactionto completion by monitoring the reaction process by gas chromatography(GC) or silica gel thin-layer chromatography (TLC). Usually, thereaction time is about 6 to 24 hours. At the end of reaction,Intermediate A is recovered from the reaction mixture through anordinary aqueous workup. If necessary, Intermediate A may be purified bya standard technique such as distillation, silica gel columnchromatography or recrystallization.

In the second step, Intermediate A, diaryl sulfide is oxidized intodiaryl sulfoxide.

The reaction may be performed by a well-known organic synthesis method,specifically by dissolving the sulfide (Intermediate A) in formic acid,acetic acid or the like, and adding aqueous hydrogen peroxide thereto.An amount of aqueous hydrogen peroxide in excess of the sulfide isaccompanied by excessive oxidation to sultone. The reaction may also beperformed by dissolving the sulfide in methylene chloride and addingm-chloroperbenzoic acid thereto. The reaction temperature is typicallyroom temperature to about 50° C. It is desirable from the standpoint ofyield that the reaction time is determined so as to drive the reactionto completion by monitoring the reaction process by GC or TLC. Usually,the reaction time is about 6 to 24 hours. At the end of reaction,Intermediate B is recovered from the reaction mixture through anordinary aqueous workup. If necessary, Intermediate B may be purified bya standard technique such as silica gel column chromatography orrecrystallization.

In the third step, a diol is reacted with the carbonyl group onIntermediate B to form cyclic acetal Intermediate C.

The reaction may be performed by a well-known organic synthesis method,specifically by dissolving Intermediate B in toluene, xylene or the likeand adding a corresponding diol thereto. The reaction rate may beincreased by adding an acid catalyst to the reaction solution. Exemplaryof the acid catalyst are hydrochloric acid, sulfuric acid, nitric acid,p-toluenesulfonic acid, methanesulfonic acid, andtrifluoromethanesulfonic acid. Also, the reaction time may be shortenedby removing the water of reaction out of the reaction system to bias theequilibrium of the reaction system to the product side. The reactiontemperature is typically about 80 to 150° C. It is desirable from thestandpoint of yield that the reaction time is determined so as to drivethe reaction to completion by monitoring the reaction process by GC orTLC. Usually, the reaction time is about 6 to 24 hours. At the end ofreaction, Intermediate C is recovered from the reaction mixture throughan ordinary aqueous workup. If necessary, Intermediate C may be purifiedby a standard technique such as silica gel column chromatography orrecrystallization.

In the 4-th step, a Grignard reagent prepared from halogenatedfluorobenzene is added to Intermediate C to form Intermediate D ortriarylsulfonium salt.

The reaction may be performed by a well-known organic synthesis method,specifically by preparing a Grignard reagent from halogenatedfluorobenzene in a standard way, adding a solution of Intermediate C ina solvent such as methylene chloride or tetrahydrofuran (THF) thereto,and adding dropwise trimethylsilyl chloride to the solution. Thereaction temperature is typically about 10 to 30° C. It is desirablefrom the standpoint of yield that the reaction time is determined so asto drive the reaction to completion by monitoring the reaction processby TLC. Usually, the reaction time is about 1 to 2 hours. At the end ofreaction, Intermediate D is recovered from the reaction mixture throughan ordinary aqueous workup. If necessary, Intermediate D may be purifiedby a standard technique such as silica gel column chromatography orrecrystallization. Notably, X⁻ in Intermediate D is preferably chlorideor bromide ion.

The 5-th step is a salt exchange between Intermediate D and IntermediateE to form Intermediate F.

The reaction may be performed by a well-known organic synthesis method,specifically by dissolving or suspending Intermediate D and IntermediateE in methylene chloride or methyl isobutyl ketone, adding water thereto,and stirring the solution or suspension. It is desirable from thestandpoint of yield to monitor the reaction process by TLC. At the endof reaction, Intermediate F is recovered from the reaction mixturethrough an ordinary aqueous workup. If necessary, Intermediate F may bepurified by a standard technique such as chromatography orrecrystallization.

In the above scheme, the 5-th step of ion exchange may be readilyperformed by any well-known method, for example, according to theteaching of JP-A 2007-145797.

The 6-th step is an aromatic nucleophilic displacement reaction ofIntermediate F to yield the desired sulfonium compound (A-a).

Specifically, the reaction is performed by suspending sodium hydride inTHF, cooling the suspension, and adding dropwise a THF solution ofIntermediate F to the system. It is desirable from the standpoint ofyield to monitor the reaction process by TLC. At the end of reaction,the sulfonium compound (A-a) is recovered from the reaction mixturethrough an ordinary aqueous workup. If necessary, the compound may bepurified by a standard technique such as chromatography orrecrystallization.

While the procedure according to the above scheme is merely exemplary,the preparation of the inventive sulfonium compound is not limitedthereto. While the scheme refers to the synthesis of a compound havingan ether bond, it is possible for the skilled artisan to synthesizesulfonium compounds having an ester bond, sulfonic ester bond, carbonatebond, and carbamate bond using any of organic chemistry methods commonlyknown in the art.

Resist Composition

Another embodiment of the invention is a chemically amplified resistcomposition comprising (A) a photoacid generator in the form of thesulfonium compound having formula (A) and (B) a base resin as essentialcomponents, and (C) an organic solvent as optional component. Ifnecessary, the resist composition may further comprise at least onecomponent selected from (D) another photoacid generator, (E) a quencher,(F) a surfactant, and (G) another component.

The amount of the PAG in the form of the sulfonium compound havingformula (A) as component (A) is preferably 0.1 to 20 parts by weight,more preferably 0.5 to 10 parts by weight per 80 parts by weight of thebase resin as component (B). As long as the amount of component (A) isin the range, good sensitivity and resolution are achievable and therisk of foreign particles being formed after development or duringstripping of resist film is avoided. The PAG may be used alone or inadmixture as component (A).

(B) Base Resin

The base resin as component (B) preferably contains recurring unitshaving the formula (a1) or recurring units having the formula (a2).

In formulae (a1) and (a2), R^(A) is each independently hydrogen,fluorine, methyl or trifluoromethyl. Z^(A) is a single bond, phenylene,naphthylene or (backbone)-C(═O)—O—Z^(A1)—, wherein Z^(A1) is a C₁-C₁₀alkanediyl group which may contain a hydroxyl moiety, ether bond, esterbond or lactone ring, or a phenylene or naphthylene group. Z^(B) is asingle bond or (backbone)-C(═O)—O—. X^(A) and X^(B) are eachindependently an acid labile group. R¹¹ is a C₁-C₂₀ monovalenthydrocarbon group which may contain a heteroatom, and n is an integer of0 to 4.

Examples of the structure of formula (a1) wherein Z^(A) is a variant areillustrated below, but not limited thereto. Herein R^(A) and X^(A) areas defined above.

A polymer comprising recurring units having formula (a1) turns alkalisoluble through the mechanism that it is decomposed under the action ofacid to generate a carboxyl group.

The acid labile groups represented by X^(A) and X^(B) may be selectedfrom a variety of such groups. Examples of the acid labile group aregroups of the following formulae (L1) to (L4), C₄-C₂₀, preferably C₄-C₁₅tertiary alkyl groups, trialkylsilyl groups in which each alkyl moietyhas 1 to 6 carbon atoms, and C₄-C₂₀ oxo-containing alkyl groups.

In formula (L1), R^(L01) and R^(L02) are each independently hydrogen ora C₁-C₁₈, preferably C₁-C₁₀ alkyl group. The alkyl group may bestraight, branched or cyclic and examples thereof include methyl, ethyl,propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl,cyclohexyl, 2-ethylhexyl, n-octyl, norbornyl, tricyclodecanyl,tetracyclododecanyl, and adamantyl.

R^(L03) is a C₁-C₁₈, preferably C₁-C₁₀ monovalent hydrocarbon groupwhich may contain a moiety containing a heteroatom such as oxygen.Examples of the monovalent hydrocarbon group include straight, branchedor cyclic alkyl groups and such groups in which some hydrogen issubstituted by hydroxyl, alkoxy, oxo, amino, alkylamino or the like, orsome carbon is replaced by a moiety containing a heteroatom such asoxygen. Suitable alkyl groups are as exemplified above for R^(L01) andR^(L02). Examples of the substituted alkyl groups are shown below.

A pair of R^(L01) and R^(L02), R^(L01) and R^(L03), or R^(L02) andR^(L03) may bond together to form a ring with the carbon and oxygenatoms to which they are attached. Each of R^(L01), R^(L02) and R^(L03)is a C₁-C₁₈, preferably C₁-C₁₀ straight or branched alkanediyl groupwhen they form a ring.

In formula (L2), R^(L04) is a C₄-C₂₀, preferably C₄-C₁₅ tertiary alkylgroup, a trialkylsilyl group in which each alkyl moiety has 1 to 6carbon atoms, a C₄-C₂₀ oxo-containing alkyl group, or a group of formula(L1). Exemplary tertiary alkyl groups include tert-butyl, tert-pentyl,1,1-diethylpropyl, 2-cyclopentylpropan-2-yl, 2-cyclohexylpropan-2-yl,2-(bicyclo[2.2.1]heptan-2-yl)propan-2-yl, 2-(adamantan-1-yl)propan-2-yl,1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethylcyclohexyl,1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl,2-methyl-2-adamantyl, and 2-ethyl-2-adamantyl. Exemplary trialkylsilylgroups include trimethylsilyl, triethylsilyl, anddimethyl-tert-butylsilyl. Exemplary oxo-containing alkyl groups include3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and 5-methyl-2-oxooxolan-5-yl.Letter x is an integer of 0 to 6.

In formula (L3), R^(L05) is an optionally substituted C₁-C₈ alkyl groupor an optionally substituted C₆-C₂₀ aryl group. The optionallysubstituted alkyl group may be straight, branched or cyclic and examplesthereof include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,tert-butyl, tert-pentyl, n-pentyl, n-hexyl, cyclopentyl and cyclohexyl,and substituted forms of the foregoing in which some hydrogen issubstituted by hydroxyl, alkoxy, carboxyl, alkoxycarbonyl, oxo, amino,alkylamino, cyano, mercapto, alkylthio, sulfo or the like. Examples ofthe optionally substituted aryl groups include phenyl, methylphenyl,naphthyl, anthryl, phenanthryl, and pyrenyl, and substituted forms ofthe foregoing in which some hydrogen is substituted by hydroxyl, alkoxy,carboxyl, alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto,alkylthio, sulfo or the like. Letter y is equal to 0 or 1, z is aninteger of 0 to 3, and 2y+z is equal to 2 or 3.

In formula (L4), R^(L06) is an optionally substituted C₁-C₈ alkyl groupor an optionally substituted C₆-C₂₀ aryl group. The alkyl group may bestraight, branched or cyclic. Examples of the alkyl and aryl groups arethe same as exemplified for R^(L05).

R^(L07) to R^(L16) are each independently hydrogen or an optionallysubstituted C₁-C₁₅ monovalent hydrocarbon group. Suitable hydrocarbongroups include straight, branched or cyclic alkyl groups such as methyl,ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-pentyl,n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl,cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl,cyclohexylethyl and cyclohexylbutyl, and substituted forms of theforegoing in which some hydrogen is substituted by hydroxyl, alkoxy,carboxyl, alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto,alkylthio, sulfo or the like. Alternatively, two of R^(L07) to R^(L16)may bond together to form a ring with the carbon atom to which they areattached (for example, a pair of R^(L07) and R^(L08), R^(L07) andR^(L09), R^(L07) and R^(L10), R^(L08) and R^(L10), R^(L09) and R^(L10),R^(L11) and R^(L12), R^(L13) and R^(L14), or a similar pair form aring). Each of R^(L07) to R^(L16) represents C₁-C₁₅ divalent hydrocarbongroup when they form a ring, examples of which are the ones exemplifiedabove for the monovalent hydrocarbon groups, with one hydrogen atombeing eliminated. Two of R^(L07) to R^(L16) which are attached tovicinal carbon atoms may bond together directly to form a double bond(for example, a pair of R^(L07) and R^(L09), R^(L09) and R^(L15),R^(L13) and R^(L15), R^(L14) and R^(L15), or a similar pair).

Of the acid labile groups having formula (L1), the straight and branchedones are exemplified by the following groups, but not limited thereto.

Of the acid labile groups having formula (L1), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Examples of the acid labile group having formula (L2) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-pentyloxycarbonyl,tert-pentyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl groups.

Examples of the acid labile group having formula (L3) include1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec-butylcyclopentyl,1-cyclohexylcyclopentyl, 1-(4-methoxy-n-butyl)cyclopentyl,1-methylcyclohexyl, 1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl groups.

Of the acid labile groups having formula (L4), groups having thefollowing formulas (L4-1) to (L4-4) are preferred.

In formulas (L4-1) to (L4-4), the broken line denotes a bonding site anddirection. R^(L21) is each independently a C₁-C₁₀ monovalent hydrocarbongroup. The monovalent hydrocarbon group may be straight, branched orcyclic, and examples thereof include alkyl groups such as methyl, ethyl,propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-pentyl,n-pentyl, n-hexyl, cyclopentyl and cyclohexyl.

For formulas (L4-1) to (L4-4), there can exist stereoisomers(enantiomers or diastereomers). Each of formulae (L4-1) to (L4-4)collectively represents all such stereoisomers. When the acid labilegroup X^(A) is of formula (L4), there may be contained a plurality ofstereoisomers.

For example, the formula (L4-3) represents one or a mixture of twoselected from groups having the following formulas (L4-3-1) and(L4-3-2).

Herein R^(L21) is as defined above.

Similarly, the formula (L4-4) represents one or a mixture of two or moreselected from groups having the following formulas (L4-4-1) to (L4-4-4).

Herein R^(L21) is as defined above.

Each of formulas (L4-1) to (L4-4), (L4-3-1), (L4-3-2), and (L4-4-1) to(L4-4-4) collectively represents an enantiomer thereof and a mixture ofenantiomers.

It is noted that in the above formulas (L4-1) to (L4-4), (L4-3-1),(L4-3-2), and (L4-4-1) to (L4-4-4), the bond direction is on the exoside relative to the bicyclo[2.2.1]heptane ring, which ensures highreactivity for acid catalyzed elimination reaction (seeJP-A2000-336121). In preparing these monomers having a tertiaryexo-alkyl group of bicyclo[2.2.1]heptane skeleton as a substituentgroup, there may be contained monomers substituted with an endo-alkylgroup as represented by the following formulas (L4-1-endo) to(L4-4-endo). For good reactivity, an exo proportion of at least 50 mol %is preferred, with an exo proportion of at least 80 mol % being morepreferred.

Herein R^(L21) is as defined above.

Illustrative examples of the acid labile group having formula (L4) aregiven below.

Examples of the tertiary C₄-C₂₀ alkyl groups, trialkylsilyl groups inwhich each alkyl moiety has 1 to 6 carbon atoms, and C₄-C₂₀oxo-containing alkyl groups, represented by X^(A), are as exemplifiedfor R^(L04).

Illustrative examples of the recurring units of formula (a1) are givenbelow, but not limited thereto. Herein R^(A) is as defined above.

The above examples correspond to those units of formula (a1) whereinZ^(A) is a single bond. Where Z^(A) is other than a single bond, acombination with a similar acid labile group is possible. Thus examplesof the recurring units of formula (a1) wherein Z^(A) is other than asingle bond are as illustrated above.

In formula (a2), the subscript n is an integer of 0 to 4, preferably 0or 1.

Like the recurring units having formula (a1), a polymer comprisingrecurring units having formula (a2) turns alkali soluble through themechanism that it is decomposed under the action of acid to generate ahydroxyl group.

Illustrative examples of the recurring units of formula (a2) are givenbelow, but not limited thereto. Herein R^(A) is as defined above.

In a preferred embodiment, the polymer further comprises recurring unitshaving the formula (b1) or (b2).

In formulae (b1) and (b2), R^(A) is as defined above, Y^(A) is hydrogenor a polar group containing at least one structure selected from amonghydroxyl, cyano, carbonyl, carboxyl, ether bond, ester bond, sulfonicacid ester bond, carbonate bond, lactone ring, sultone ring andcarboxylic anhydride, and m is 1 or 2.

Examples of the recurring unit having formula (b1) are shown below, butnot limited thereto. Herein, R^(A) is as defined above.

Examples of the recurring unit having formula (b2) are shown below, butnot limited thereto. Herein, R^(A) is as defined above.

Of the recurring units having formula (b1) or (b2), those units having alactone ring as the polar group are preferred in the ArF lithography andthose units having a phenolic site are preferred in the KrF, EB and EUVlithography.

The polymer may further comprise recurring units of at least one typeselected from recurring units having the formulae (c1) to (c3).

In formulae (c1) to (c3), R^(A) is as defined above. Z¹ is a singlebond, phenylene, —O—Z¹¹—, —C(═O)—O—Z¹¹— or —C(═O)—NH—Z¹¹—, wherein Z¹¹is a C₁-C₂₀ alkanediyl group, C₂-C₂₀ alkenediyl group or phenylenegroup, which may contain a carbonyl moiety (—CO—), ester bond (—COO—),ether bond (—O—) or hydroxyl moiety. Z² is a single bond or—Z²¹—C(═O)—O— wherein Z²¹ is a C₁-C₂₀ divalent hydrocarbon group whichmay contain a heteroatom. Z³ is a single bond, methylene, ethylene,phenylene, fluorinated phenylene, —O—Z³¹—, —C(═O)—O—Z³¹— or—C(═O)—NH—Z³¹—, wherein Z³¹ is a C₁-C₆ alkanediyl group, C₂-C₆alkenediyl group or phenylene group, which may contain a carbonylmoiety, ester bond, ether bond or hydroxyl moiety.

In formula (c1), R²¹ and R²² are each independently a C₁-C₂₀ monovalenthydrocarbon group which may contain a heteroatom. R²¹ and R²² may bondtogether to form a ring with the sulfur atom to which they are attached.

Examples of the monovalent hydrocarbon group represented by R²¹ and R²²include alkyl groups such as methyl, ethyl, n-propyl, isopropyl,n-butyl, tert-butyl, cyclopropyl, cyclopentyl, cyclohexyl,cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, andadamantyl, alkenyl groups such as vinyl, allyl, propenyl, butenyl,hexenyl, and cyclohexenyl, aryl groups such as phenyl, naphthyl, andthienyl, and aralkyl groups such as benzyl, 1-phenylethyl and2-phenylethyl. Inter alia, aryl groups are preferred. In thesehydrocarbon groups, some hydrogen may be substituted by a moietycontaining a heteroatom such as oxygen, sulfur, nitrogen or halogen, anda moiety containing a heteroatom such as oxygen, sulfur or nitrogen mayintervene between carbon atoms, so that the group may contain a hydroxylmoiety, cyano moiety, carbonyl moiety, ether bond, ester bond, sulfonicacid ester bond, carbonate bond, lactone ring, sultone ring, carboxylicanhydride or haloalkyl moiety.

In formula (c1), M⁻ is a non-nucleophilic counter ion. Examples of thenon-nucleophilic counter ion include halide ions such as chloride andbromide ions; fluoroalkylsulfonate ions such as triflate,1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate;arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate;alkylsulfonate ions such as mesylate and butanesulfonate; imide ionssuch as bis(trifluoromethylsulfonyl)imide,bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imide;and methide ions such as tris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

Also included are a sulfonate anion which is fluorinated at α-positionas represented by the formula (c1-1) and a sulfonate anion which isfluorinated at α- and β-positions as represented by the formula (c1-2).

In formula (c1-1), R³¹ is hydrogen, or a C₁-C₂₀ alkyl group, C₂-C₂₀alkenyl group or C₆-C₂₀ aryl group, which may contain an ether bond,ester bond, carbonyl moiety, lactone ring or fluorine atom. The alkyland alkenyl groups may be straight, branched or cyclic.

In formula (c1-2), R³² is hydrogen, or a C₁-C₃₀ alkyl group, C₂-C₃₀ acylgroup, C₂-C₂₀ alkenyl group, C₆-C₂₀ aryl group or C₆-C₂₀ aryloxy group,which may contain an ether bond, ester bond, carbonyl moiety or lactonering. The alkyl, acyl, and alkenyl groups may be straight, branched orcyclic.

In formula (c2) wherein Z² is —Z²¹—C(═O)—O—, Z²¹ is a C₁-C₂₀ divalenthydrocarbon group which may contain a heteroatom. Examples of thedivalent hydrocarbon group are shown below, but not limited thereto.

In formulae (c2) and (c3), A⁺ is a sulfonium cation or iodonium cation.Suitable examples of the sulfonium or iodonium cation include sulfoniumcations having the formula (c4) or iodonium cations having the formula(c5).

In formula (c4), R⁴¹, R⁴² and R⁴³ are each independently a C₁-C₂₀monovalent hydrocarbon group which may contain a heteroatom. Any two ofR⁴¹, R⁴² and R⁴³ may bond together to form a ring with the sulfur atomto which they are attached. In formula (c5), R⁴⁴ and R⁴⁵ are eachindependently a C₁-C₂₀ monovalent hydrocarbon group which may contain aheteroatom.

The monovalent hydrocarbon group may be straight, branched or cyclic.Examples include alkyl groups such as methyl, ethyl, n-propyl,isopropyl, n-butyl, tert-butyl, cyclopropyl, cyclopentyl, cyclohexyl,cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, andadamantyl, alkenyl groups such as vinyl, allyl, propenyl, butenyl,hexenyl, and cyclohexenyl, aryl groups such as phenyl, naphthyl, andthienyl, and aralkyl groups such as benzyl, 1-phenylethyl and2-phenylethyl. Inter alia, aryl groups are preferred. In thesemonovalent hydrocarbon groups, some hydrogen may be substituted by amoiety containing a heteroatom such as oxygen, sulfur, nitrogen orhalogen, and a moiety containing a heteroatom such as oxygen, sulfur ornitrogen may intervene between carbon atoms, so that the group maycontain a hydroxyl moiety, cyano moiety, carbonyl moiety, ether bond,ester bond, sulfonic acid ester bond, carbonate bond, lactone ring,sultone ring, carboxylic anhydride or haloalkyl moiety.

When any two of R⁴¹, R⁴² and R⁴³ bond together to form a ring with thesulfur atom to which they are attached, examples of the sulfonium cationhaving formula (c4) are shown below.

Herein R⁴⁶ is a C₁-C₂₀ monovalent hydrocarbon group which may contain aheteroatom.

Examples of the sulfonium cation having formula (c4) are given below,but not limited thereto.

Examples of the iodonium cation having formula (c5) are given below, butnot limited thereto.

The polymer may further comprise recurring units of a structure having ahydroxyl group protected with an acid labile group. These recurringunits are not particularly limited as long as the unit includes one ormore structures having a hydroxyl group protected with a protectivegroup such that the protective group is decomposed to generate thehydroxyl group under the action of acid. Recurring units having theformula (d1) are preferred.

In formula (d1), R^(A) is as defined above. R⁵¹ is a C₁-C₃₀ (j+1)-valenthydrocarbon group which may contain a heteroatom. R⁵² is an acid labilegroup, and j is an integer of 1 to 4.

Examples of the recurring units having formula (d1) are shown below, butnot limited thereto. Herein R^(A) and R⁵² are as defined above.

The acid labile group R⁵² in formula (d1) is not particularly limited aslong as it is deprotected to generate a hydroxyl group under the actionof acid. Typical, non-limiting acid labile groups are groups of acetalor ketal structure and alkoxycarbonyl groups, with examples being shownbelow.

Of the acid labile groups R⁵², alkoxymethyl groups having the formula(d2) are preferred.

Herein R⁵³ is a C₁-C₁₅ monovalent hydrocarbon group.

Examples of the acid labile group having formula (d2) are shown below,but not limited thereto.

In addition to the foregoing units, the polymer may further compriserecurring units derived from other monomers, for example, substitutedacrylic acid esters such as methyl methacrylate, methyl crotonate,dimethyl maleate and dimethyl itaconate, unsaturated carboxylic acidssuch as maleic acid, fumaric acid, and itaconic acid, cyclic olefinssuch as norbornene, norbomene derivatives, andtetracyclo[6.2.1.1^(3,6).0^(2,7)]dodecene derivatives, and unsaturatedacid anhydrides such as itaconic anhydride.

The polymer preferably has a weight average molecular weight (Mw) of1,000 to 500,000, and more preferably 3,000 to 100,000, as measuredversus polystyrene standards by gel permeation chromatography (GPC)using tetrahydrofuran (THF) as solvent. The above range of Mw ensuressatisfactory etch resistance and eliminates the risk of resolution beingreduced due to difficulty to gain a dissolution rate difference beforeand after exposure.

If a polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof Mw and Mw/Mn become stronger as the pattern rule becomes finer.Therefore, the polymer should preferably have a narrow dispersity(Mw/Mn) of 1.0 to 2.0 in order to provide a resist composition suitablefor micropatterning to a small feature size.

The method of synthesizing the polymer is, for example, by dissolvingone or more unsaturated bond-bearing monomers in an organic solvent,adding a radical initiator, and heating for polymerization. Examples ofthe organic solvent which can be used for polymerization includetoluene, benzene, THF, diethyl ether and dioxane. Examples of thepolymerization initiator used herein include 2,2′-azobisisobutyronitrile(AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the reaction temperature is 50 to 80° C. The reaction time ispreferably 2 to 100 hours, more preferably 5 to 20 hours. The acidlabile group that has been incorporated in the monomer may be kept assuch, or polymerization may be followed by protection or partialprotection.

While the polymer comprises recurring units derived from monomers, themolar fractions of respective units preferably fall in the followingrange (mol %), but are not limited thereto:

-   (I) 1 to 60 mol %, more preferably 5 to 50 mol %, even more    preferably 10 to 50 mol % of recurring units of at least one type    having formula (a1) or (a2),-   (II) 40 to 99 mol %, more preferably 50 to 95 mol %, even more    preferably 50 to 90 mol % of recurring units of at least one type    having formula (b1) or (b2), and optionally,-   (III) 0 to 30 mol %, more preferably 0 to 20 mol %, and even more    preferably 0 to 10 mol % of recurring units of at least one type    selected from formulae (c1) to (c3), and optionally,-   (IV) 0 to 80 mol %, more preferably 0 to 70 mol %, and even more    preferably 0 to 50 mol % of recurring units of at least one type    derived from another monomer(s).

The polymers may be used as the base resin (B) alone or in a combinationof two or more polymers which are different in compositional ratio, Mwand/or Mw/Mn. In addition to the foregoing polymer, the base resin (B)may contain a hydrogenated ROMP polymer as described in JP-A2003-066612.

(C) Organic Solvent

Any organic solvent may be used as long as the foregoing components andother additives are soluble therein. Examples of the organic solvent aredescribed in JP-A 2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No.7,537,880). Specifically, exemplary solvents include ketones such ascyclohexanone and methyl-2-n-pentyl ketone; alcohols such as3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol,1-ethoxy-2-propanol, and diacetone alcohol (DAA); ethers such aspropylene glycol monomethyl ether, ethylene glycol monomethyl ether,propylene glycol monoethyl ether, ethylene glycol monoethyl ether,propylene glycol dimethyl ether, and diethylene glycol dimethyl ether;esters such as propylene glycol monomethyl ether acetate (PGMEA),propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate,butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate,tert-butyl acetate, tert-butyl propionate, and propylene glycolmono-tert-butyl ether acetate; and lactones such as γ-butyrolactone(GBL), and mixtures thereof. Where an acid labile group of acetal formis used, a high-boiling alcohol solvent such as diethylene glycol,propylene glycol, glycerol, 1,4-butanediol or 1,3-butanediol may beadded for accelerating deprotection reaction of acetal. Of the aboveorganic solvents, it is recommended to use DAA, 1-ethoxy-2-propanol,PGMEA, cyclohexanone, GBL, and mixtures thereof because the PAG (A) ismost soluble therein.

An appropriate amount of the organic solvent used is 200 to 5,000 parts,more preferably 400 to 3,000 parts by weight per 80 parts by weight ofthe base resin (B).

(D) Other Photoacid Generator

The chemically amplified resist composition may comprise (D) a photoacidgenerator other than component (A). The other photoacid generator is notparticularly limited as long as it is capable of generating an acid uponexposure to high-energy radiation. The preferred other photoacidgenerator is a salt having the formula (1).

In formula (1), R¹⁰¹, R¹⁰² and R¹⁰³ are each independently a C₁-C₂₀monovalent hydrocarbon group which may contain a heteroatom. Any two ofR¹⁰¹, R¹⁰² and R¹⁰³ may bond together to form a ring with the sulfuratom to which they are attached. The monovalent hydrocarbon group may bestraight, branched or cyclic and examples thereof areas exemplifiedabove in conjunction with formula (c4). Examples of the cation in thesulfonium salt of formula (1) are as exemplified above for the sulfoniumcation having formula (c4).

In formula (1), X⁻ is an anion selected from the formulae (1A) to (1D).

In formula (1A), R^(fa) is fluorine or a C₁-C₄₀ monovalent hydrocarbongroup which may contain a heteroatom. The monovalent hydrocarbon groupmay be straight, branched or cyclic and examples thereof are as will beexemplified later for R¹¹² in formula (1A′).

Of the anions having formula (1A), a structure having the formula (1A′)is preferred.

In formula (1A′), R¹¹¹ is hydrogen or trifluoromethyl, preferablytrifluoromethyl.

R¹¹² is a C₁-C₃₈ monovalent hydrocarbon group which may contain aheteroatom.

Suitable heteroatoms include oxygen, nitrogen, sulfur and halogen, withoxygen being preferred. Of the monovalent hydrocarbon groups, those of 6to 30 carbon atoms are preferred because a high resolution is availablein fine pattern formation. The monovalent hydrocarbon group may bestraight, branched or cyclic. Examples include methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl,cyclopentyl, hexyl, cyclohexyl, 3-cyclohexenyl, heptyl, 2-ethylhexyl,nonyl, undecyl, tridecyl, pentadecyl, heptadecyl, 1-adamantyl,2-adamantyl, 1-adamantylmethyl, norbornyl, norbomylmethyl,tricyclodecanyl, tetracyclododecanyl, tetracyclododecanylmethyl,dicyclohexylmethyl, icosanyl, allyl, benzyl, diphenylmethyl,tetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl,acetamidomethyl, trifluoroethyl, (2-methoxyethoxy)methyl, acetoxymethyl,2-carboxy-1-cyclohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and3-oxocyclohexyl. In these groups, some hydrogen may be substituted by amoiety containing a heteroatom such as oxygen, sulfur, nitrogen orhalogen, or a moiety containing a heteroatom such as oxygen, sulfur ornitrogen may intervene between carbon atoms, so that the group maycontain a hydroxyl, cyano, carbonyl, ether bond, ester bond, sulfonicacid ester bond, carbonate bond, lactone ring, sultone ring, carboxylicanhydride or haloalkyl moiety.

With respect to the synthesis of the sulfonium salt having an anion offormula (1A′), reference is made to JP-A 2007-145797, JP-A 2008-106045,JP-A 2009-007327, and JP-A 2009-258695. Also useful are the sulfoniumsalts described in JP-A 2010-215608, JP-A 2012-041320, JP-A 2012-106986,and JP-A 2012-153644.

Examples of the anion having formula (1A) are shown below, but notlimited thereto.

In formula (1B), R^(fb1) and R^(fb2) are each independently fluorine ora C₁-C₄₀ monovalent hydrocarbon group which may contain a heteroatom.The monovalent hydrocarbon groups may be straight, branched or cyclic,and examples thereof are as exemplified above for R¹¹². PreferablyR^(fb1) and R^(fb2) each are fluorine or a straight C₁-C₄ fluorinatedalkyl group. A pair of R^(fb1) and R^(fb2) may bond together to form aring with the linkage (—CF₂—SO₂—N⁻—SO₂—CF₂—) to which they are attached,and preferably the pair is a fluorinated ethylene or fluorinatedpropylene group.

In formula (1C), R^(fc1), R^(fc2) and R^(fc3) are each independentlyfluorine or a C₁-C₄₀ monovalent hydrocarbon group which may contain aheteroatom. The monovalent hydrocarbon group may be straight, branchedor cyclic, and examples thereof are as exemplified above for R¹¹².Preferably R^(fc1), R^(fc2) and R^(fc3) each are fluorine or a straightC₁-C₄ fluorinated alkyl group. A pair of R^(fc1) and R^(fc2) may bondtogether to form a ring with the linkage (—CF₂—SO₂—C⁻—SO₂—CF₂—) to whichthey are attached, and preferably the pair is a fluorinated ethylene orfluorinated propylene group.

In formula (1D), R^(fd) is a C₁-C₄₀ monovalent hydrocarbon group whichmay contain a heteroatom. The monovalent hydrocarbon group may bestraight, branched or cyclic, and examples thereof are as exemplifiedabove for R¹¹².

With respect to the synthesis of the sulfonium salt having an anion offormula (1D), reference is made to JP-A 2010-215608 and JP-A2014-133723.

Examples of the anion having formula (1D) are shown below, but notlimited thereto.

The compound having the anion of formula (1D) has a sufficient acidstrength to cleave acid labile groups in the resist polymer because itis free of fluorine at α-position of sulfo group, but has twotrifluoromethyl groups at β-position. Thus the compound is a useful PAG.

Further, compounds having the formula (2) are also useful as the PAG(D).

In formula (2), R²⁰¹ and R²⁰² are each independently a C₁-C₃₀ monovalenthydrocarbon group which may contain a heteroatom. R²⁰³ is a C₁-C₃₀divalent hydrocarbon group which may contain a heteroatom. Any two ofR²⁰¹, R²⁰² and R²⁰³ may bond together to form a ring with the sulfuratom to which they are attached. L^(A) is a single bond or ether bond,or a C₁-C₂₀ divalent hydrocarbon group which may contain a heteroatom.X^(a), X^(b), X^(c) and X^(d) are each independently hydrogen, fluorineor trifluoromethyl, with the proviso that at least one of X^(a), X^(b),X^(c) and X^(d) is fluorine or trifluoromethyl.

The monovalent hydrocarbon groups represented by R²⁰¹ and R²⁰² may bestraight, branched or cyclic, and examples thereof include methyl,ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl,tert-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl,cyclohexyl, 2-ethylhexyl, cyclopentylmethyl, cyclopentylethyl,cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl,norbornyl, oxanorbornyl, tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl,phenyl, naphthyl, and anthracenyl. Also included are the foregoinggroups in which some hydrogen is substituted by a moiety containing aheteroatom such as oxygen, sulfur, nitrogen or halogen, or in which amoiety containing a heteroatom such as oxygen, sulfur or nitrogenintervenes between carbon atoms, so that the group may contain ahydroxyl, cyano, carbonyl, ether bond, ester bond, sulfonic acid esterbond, carbonate bond, lactone ring, sultone ring, carboxylic anhydrideor haloalkyl moiety.

The divalent hydrocarbon groups represented by R²⁰³ include straightalkanediyl groups such as methylene, ethylene, propane-1,3-diyl,butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl,octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl,dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl,pentadecane-1,15-diyl, hexadecane-1,16-diyl, heptadecane-1,17-diyl;arylene groups such as cyclopentanediyl, cyclohexanediyl, norbomanediyl,and adamantanediyl; and divalent unsaturated cyclic hydrocarbon groupssuch as phenylene and naphthylene. Also included are the foregoinggroups in which some hydrogen is substituted by an alkyl group such asmethyl, ethyl, propyl, n-butyl or tert-butyl, or in which some hydrogenis substituted by a moiety containing a heteroatom such as oxygen,sulfur, nitrogen or halogen, or in which a moiety containing aheteroatom such as oxygen, sulfur or nitrogen intervenes between carbonatoms, so that the group may contain a hydroxyl, cyano, carbonyl, etherbond, ester bond, sulfonic acid ester bond, carbonate bond, lactonering, sultone ring, carboxylic anhydride or haloalkyl moiety. Thepreferred heteroatom is oxygen.

Of the PAGs having formula (2), those compounds having formula (2′) arepreferred.

In formula (2′), L^(A) is as defined above. X^(e) is hydrogen ortrifluoromethyl, preferably trifluoromethyl. R³⁰¹, R³⁰² and R³⁰³ areeach independently hydrogen or a C₁-C₂₀ monovalent hydrocarbon groupwhich may contain a heteroatom. The monovalent hydrocarbon group may bestraight, branched or cyclic, and examples thereof are as exemplifiedabove for R¹¹². The subscripts p and q each are an integer of 0 to 5,and r is an integer of 0 to 4.

Examples of the PAG having formula (2) are shown below, but not limitedthereto. Herein X^(e) is as defined above.

Of the other PAGs, those compounds having an anion of formula (1A′) or(1D) are especially preferred because of reduced acid diffusion and highsolubility in resist solvent, and those compounds having an anion offormula (2′) are especially preferred because of minimized aciddiffusion.

When the resist composition contains the other PAG (D), an appropriateamount of the PAG added is 0.1 to 40 parts, more preferably 0.5 to 20parts by weight per 80 parts by weight of the base resin (B). As long asthe amount of component (D) is in the range, good resolution isachievable and the risk of foreign particles being formed afterdevelopment or during stripping of resist film is avoided. The other PAGmay be used alone or in admixture as component (D).

(E) Quencher

The chemically amplified resist composition may further include (E) aquencher or acid diffusion controlling agent. As used herein, the“quencher” refers to a compound capable of trapping the acid generatedby the PAG in the resist film to prevent the acid from diffusing to theunexposed region thereof, for thereby forming the desired pattern.

Typical of the quencher (E) are onium salts having the formulae (3) and(4).R^(q1)—SO₃ ⁻Mq⁺  (3)R^(q2)—CO₂ ⁻Mq⁺  (4)

In formula (3), R^(q1) is hydrogen or a C₁-C₄₀ monovalent hydrocarbongroup which may contain a heteroatom, exclusive of the group whereinhydrogen bonded to the carbon atom at α-position relative to the sulfogroup is substituted by fluorine or fluoroalkyl. In formula (4), R^(q2)is hydrogen or a C₁-C₄₀ monovalent hydrocarbon group which may contain aheteroatom. The monovalent hydrocarbon group may be straight, branchedor cyclic and examples thereof are as exemplified above for R¹¹² informula (1A′).

Examples of the monovalent hydrocarbon group R^(q1) include methyl,ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl,tert-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl,cyclohexyl, 2-ethylhexyl, cyclopentylmethyl, cyclopentylethyl,cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl,norbornyl, oxanorbomyl, tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl,phenyl, naphthyl, and anthracenyl.

In these groups, some hydrogen may be substituted by a moiety containinga heteroatom such as oxygen, sulfur, nitrogen or halogen, and a moietycontaining a heteroatom such as oxygen, sulfur or nitrogen may intervenebetween carbon atoms, so that the group may contain a hydroxyl moiety,cyano moiety, carbonyl moiety, ether bond, ester bond, sulfonic acidester bond, carbonate bond, lactone ring, sultone ring, carboxylicanhydride, or haloalkyl moiety.

Examples of the monovalent hydrocarbon group R^(q2) include fluoroalkylgroups such as trifluoromethyl and trifluoroethyl and fluoroaryl groupssuch as pentafluorophenyl and 4-trifluoromethylphenyl as well as thesubstituents exemplified above for R^(q1).

Examples of the anion in the onium salt having formula (3) are shownbelow, but not limited thereto.

Examples of the anion in the onium salt having formula (4) are shownbelow, but not limited thereto.

In formulae (3) and (4), Mq⁺ is an onium cation, which is preferablyselected from cations having the formulae (5a), (5b) and (5c).

In formulae (5a) to (5c), R^(q11) to R^(q19) are each independently aC₁-C₄₀ monovalent hydrocarbon group which may contain a heteroatom. Apair of R^(q11) and R^(q12) may bond together to form a ring with thesulfur atom to which they are attached. A pair of R^(q16) and R^(q17)may bond together to form a ring with the nitrogen atom to which theyare attached. Examples of the monovalent hydrocarbon group are asexemplified above for R^(q1) in formula (3).

Examples of the onium cation represented by Mq⁺ are shown below, but notlimited thereto.

Examples of the onium salt having formula (3) or (4) include arbitrarycombinations of anions with cations, both as exemplified above. Theseonium salts may be readily obtained from ion exchange reaction using anywell-known organic chemistry technique. For the ion exchange reaction,reference may be made to JP-A 2007-145797, for example.

The onium salt having formula (3) or (4) functions as a quencher in thechemically amplified resist composition because the counter anion of theonium salt is a conjugated base of a weak acid. As used herein, the weakacid indicates an acidity insufficient to deprotect an acid labile groupfrom an acid labile group-containing unit in the base resin. The oniumsalt having formula (3) or (4) functions as a quencher when used incombination with an onium salt type PAG having a conjugated base of astrong acid (typically a sulfonic acid which is fluorinated atα-position) as the counter anion. In a system using a mixture of anonium salt capable of generating a strong acid (e.g., α-positionfluorinated sulfonic acid) and an onium salt capable of generating aweak acid (e.g., non-fluorinated sulfonic acid or carboxylic acid), ifthe strong acid generated from the PAG upon exposure to high-energyradiation collides with the unreacted onium salt having a weak acidanion, then a salt exchange occurs whereby the weak acid is released andan onium salt having a strong acid anion is formed. In this course, thestrong acid is exchanged into the weak acid having a low catalysis,incurring apparent deactivation of the acid for enabling to control aciddiffusion.

If a PAG capable of generating a strong acid is an onium salt, anexchange from the strong acid generated upon exposure to high-energyradiation to a weak acid as above can take place, but it rarely happensthat the weak acid generated upon exposure to high-energy radiationcollides with the unreacted onium salt capable of generating a strongacid to induce a salt exchange. This is because of a likelihood of anonium cation forming an ion pair with a stronger acid anion.

When the onium salt having formula (3) or (4) is used as the quencher(E), the amount of the onium salt used is preferably 0.1 to 10 parts byweight, more preferably 0.1 to 5 parts by weight per 80 parts by weightof the base resin (B). As long as the amount of component (E) is in therange, a satisfactory resolution is available without a substantiallowering of sensitivity. The onium salt having formula (3) or (4) may beused alone or in admixture.

Also nitrogen-containing compounds may be used as the quencher (E).Suitable nitrogen-containing compounds include primary, secondary andtertiary amine compounds, specifically amine compounds having a hydroxylgroup, ether bond, ester bond, lactone ring, cyano group or sulfonatebond, as described in JP-A 2008-111103, paragraphs [0146]-[0164] (U.S.Pat. No. 7,537,880), and primary or secondary amine compounds protectedwith a carbamate group, as described in JP 3790649.

A sulfonic acid sulfonium salt having a nitrogen-containing substituentmay also be used as the nitrogen-containing compound. This compoundfunctions as a quencher in the unexposed region, but as a so-calledphoto-degradable base in the exposed region because it loses thequencher function in the exposed region due to neutralization thereofwith the acid generated by itself. Using a photo-degradable base, thecontrast between exposed and unexposed regions can be further enhanced.With respect to the photo-degradable base, reference may be made to JP-A2009-109595 and JP-A 2012-046501, for example.

When the nitrogen-containing compound is used as the quencher (E), theamount of the nitrogen-containing compound used is preferably 0.001 to12 parts by weight, more preferably 0.01 to 8 parts by weight per 80parts by weight of the base resin (B). The nitrogen-containing compoundmay be used alone or in admixture.

(F) Surfactant

The resist composition may further include (F) a surfactant which isinsoluble or substantially insoluble in water and soluble in alkalinedeveloper, and/or a surfactant (hydrophobic resin) which is insoluble orsubstantially insoluble in water and alkaline developer. For thesurfactant, reference should be made to those compounds described inJP-A 2010-215608 and JP-A 2011-016746.

While many examples of the surfactant which is insoluble orsubstantially insoluble in water and alkaline developer are described inthe patent documents cited herein, preferred examples are fluorochemicalsurfactants FC-4430 (3M), Olfine® E1004 (Nissin Chemical Co., Ltd.),Surflon® S-381, KH-20 and KH-30 (AGC Seimi Chemical Co., Ltd.).Partially fluorinated oxetane ring-opened polymers having the formula(surf-1) are also useful.

It is provided herein that R, Rf, A, B, C, m, and n are applied to onlyformula (surf-1), independent of their descriptions other than for thesurfactant. R is a di- to tetra-valent C₂-C₅ aliphatic group. Exemplarydivalent aliphatic groups include ethylene, 1,4-butylene, 1,2-propylene,2,2-dimethyl-1,3-propylene and 1,5-pentylene. Exemplary tri- andtetra-valent groups are shown below.

Herein the broken line denotes a valence bond. These formulae arepartial structures derived from glycerol, trimethylol ethane,trimethylol propane, and pentaerythritol, respectively. Of these,1,4-butylene and 2,2-dimethyl-1,3-propylene are preferably used.

Rf is trifluoromethyl or pentafluoroethyl, and preferablytrifluoromethyl. The letter m is an integer of 0 to 3, n is an integerof 1 to 4, and the sum of m and n, which represents the valence of R, isan integer of 2 to 4. “A” is equal to 1, B is an integer of 2 to 25, andC is an integer of 0 to 10. Preferably, B is an integer of 4 to 20, andC is 0 or 1. Note that the formula (surf-1) does not prescribe thearrangement of respective constituent units while they may be arrangedeither blockwise or randomly. For the preparation of surfactants in theform of partially fluorinated oxetane ring-opened polymers, referenceshould be made to U.S. Pat. No. 5,650,483, for example.

The surfactant which is insoluble or substantially insoluble in waterand soluble in alkaline developer is useful when ArF immersionlithography is applied to the resist composition in the absence of aresist protective film. In this embodiment, the surfactant has apropensity to segregate on the resist surface after spin coating forachieving a function of minimizing water penetration or leaching. Thesurfactant is also effective for preventing water-soluble componentsfrom being leached out of the resist film for minimizing any damage tothe exposure tool. The surfactant becomes solubilized during alkalinedevelopment following exposure and PEB, and thus forms few or no foreignparticles which become defects. The preferred surfactant is a polymericsurfactant which is insoluble or substantially insoluble in water, butsoluble in alkaline developer, also referred to as “hydrophobic resin”in this sense, and especially which is water repellent and enhanceswater sliding.

Suitable polymeric surfactants include those containing recurring unitsof at least one type selected from the formulae (6A) to (6E).

Herein, R^(B) is hydrogen, fluorine, methyl or trifluoromethyl. W¹ is—CH₂—, —CH₂CH₂— or —O—, or two separate —H. R^(s1) is each independentlyhydrogen or a C₁-C₁₀ monovalent hydrocarbon group. R^(s2) is a singlebond or a C₁-C₅ straight or branched divalent hydrocarbon group. R^(s3)is each independently hydrogen, a C₁-C₁₅ monovalent hydrocarbon orfluorinated hydrocarbon group, or an acid labile group. When R^(s3) is amonovalent hydrocarbon or fluorinated hydrocarbon group, an ether bond(—O—) or carbonyl moiety (—C(═O)—) may intervene in a carbon-carbonbond. R^(s4) is a C₁-C₂₀ (u+1)-valent hydrocarbon or fluorinatedhydrocarbon group, and u is an integer of 1 to 3. R^(s5) is eachindependently hydrogen or a group having the formula: —C(═O)—O—R^(sa)wherein R^(sa) is a C₁-C₂₀ fluorinated hydrocarbon group. R^(s6) is aC₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbon group in whichan ether bond (—O—) or carbonyl moiety (—C(═O)—) may intervene in acarbon-carbon bond.

The monovalent hydrocarbon group represented by R^(s1) may be straight,branched or cyclic and examples thereof include methyl, ethyl, n-propyl,isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl,cyclobutyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl,n-octyl, n-nonyl, n-decyl, adamantyl, and norbomyl. Inter alia, C₁-C₆hydrocarbon groups are preferred.

The divalent hydrocarbon group represented by R^(s2) may be straight,branched or cyclic and examples thereof include methylene, ethylene,propylene, butylene, and pentylene.

The monovalent hydrocarbon group represented by R^(s3) or R^(s6) may bestraight, branched or cyclic and examples thereof include alkyl,alkenyl, and alkynyl groups, with the alkyl groups being preferred.Suitable alkyl groups include those exemplified for the monovalenthydrocarbon group represented by R^(s1) as well as n-undecyl, n-dodecyl,tridecyl, tetradecyl, and pentadecyl. Examples of the monovalentfluorinated hydrocarbon group represented by R^(s3) or R^(s6) includethe foregoing monovalent hydrocarbon groups in which some or allcarbon-bonded hydrogen atoms are substituted by fluorine atoms. In thesegroups, an ether bond (—O—) or carbonyl moiety (—C(═O)—) may intervenein a carbon-carbon bond as mentioned above.

Examples of the acid labile group represented by R^(s3) include groupsof the above formulae (L1) to (L4), C₄-C₂₀, preferably C₄-C₁₅ tertiaryalkyl groups, trialkylsilyl groups in which each alkyl moiety has 1 to 6carbon atoms, and C₄-C₂₀ oxo-containing alkyl groups.

The (u+1)-valent hydrocarbon or fluorinated hydrocarbon grouprepresented by R^(s4) may be straight, branched or cyclic and examplesthereof include the foregoing monovalent hydrocarbon or fluorinatedhydrocarbon groups from which the number (u) of hydrogen atoms areeliminated.

The fluorinated hydrocarbon group represented by R^(sa) may be straight,branched or cyclic and examples thereof include the foregoing monovalenthydrocarbon groups in which some or all hydrogen atoms are substitutedby fluorine atoms. Illustrative examples include trifluoromethyl,2,2,2-trifluoroethyl, 3,3,3-trifluoro-1-propyl,3,3,3-trifluoro-2-propyl, 2,2,3,3-tetrafluoropropyl,1,1,1,3,3,3-hexafluoroisopropyl, 2,2,3,3,4,4,4-heptafluorobutyl,2,2,3,3,4,4,5,5-octafluoropentyl,2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, 2-(perfluorobutyl)ethyl,2-(perfluorohexyl)ethyl, 2-(perfluorooctyl)ethyl, and2-(perfluorodecyl)ethyl.

Examples of the recurring units having formulae (6A) to (6E) are shownbelow, but not limited thereto. Herein R^(B) is as defined above.

The polymeric surfactant may further contain recurring units other thanthe recurring units having formulae (6A) to (6E). Typical otherrecurring units are those derived from methacrylic acid andα-trifluoromethylacrylic acid derivatives. In the polymeric surfactant,the content of the recurring units having formulae (6A) to (6E) ispreferably at least 20 mol %, more preferably at least 60 mol %, mostpreferably 100 mol % of the overall recurring units.

The polymeric surfactant preferably has a Mw of 1,000 to 500,000, morepreferably 3,000 to 100,000 and a Mw/Mn of 1.0 to 2.0, more preferably1.0 to 1.6.

The polymeric surfactant may be synthesized by any desired method, forexample, by dissolving an unsaturated bond-containing monomer ormonomers providing recurring units having formula (6A) to (6E) andoptionally other recurring units in an organic solvent, adding a radicalinitiator, and heating for polymerization. Suitable organic solventsused herein include toluene, benzene, THF, diethyl ether, and dioxane.Examples of the polymerization initiator used herein include AIBN,2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the reaction temperature is 50 to 100° C. and the reactiontime is 4 to 24 hours. The acid labile group that has been incorporatedin the monomer may be kept as such, or the polymer may be protected orpartially protected therewith at the end of polymerization.

During the synthesis of polymeric surfactant, any known chain transferagent such as dodecyl mercaptan or 2-mercaptoethanol may be added formolecular weight control purpose. The amount of chain transfer agentadded is preferably 0.01 to 10 mol % based on the total moles ofmonomers to be polymerized.

When the resist composition contains a surfactant (F), the amountthereof is preferably 0.1 to 50 parts by weight, and more preferably 0.5to 10 parts by weight per 80 parts by weight of the base resin (B). Atleast 0.1 part of the surfactant is effective in improving the recedingcontact angle with water of the resist film at its surface. Up to 50parts of the surfactant is effective in forming a resist film having alow rate of dissolution in an alkaline developer and capable ofmaintaining the height of a fine pattern formed therein.

(G) Other Components

The resist composition may further comprise (G) another component, forexample, a compound which is decomposed with an acid to generate anotheracid (i.e., acid amplifier compound), an organic acid derivative, afluorinated alcohol, and a compound having a Mw of up to 3,000 whichchanges its solubility in developer under the action of an acid (i.e.,dissolution inhibitor). Specifically, the acid amplifier compound isdescribed in JP-A 2009-269953 and JP-A 2010-215608 and preferably usedin an amount of 0 to 5 parts, more preferably 0 to 3 parts by weight per80 parts by weight of the base resin (B). An extra amount of the acidamplifier compound can make the acid diffusion control difficult andcause degradations to resolution and pattern profile. With respect tothe remaining additives, reference should be made to JP-A 2009-269953and JP-A 2010-215608.

Process

A further embodiment of the invention is a pattern forming process usingthe chemically amplified resist composition defined above. A pattern maybe formed from the resist composition using any well-known lithographyprocess. The preferred process includes the steps of applying the resistcomposition to form a resist film on a substrate, exposing a selectedregion of the resist film to KrF excimer laser, ArF excimer laser, EB orEUV, and developing the exposed resist film in a developer. Any desiredsteps may be added to the process if necessary.

The substrate used herein may be a substrate for integrated circuitryfabrication, e.g., Si, SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, organicantireflective film, etc. or a substrate for mask circuitry fabrication,e.g., Cr, CrO, CrON, MoSi₂, SiO₂, etc.

The resist composition is applied onto a substrate by a suitable coatingtechnique such as spin coating. The coating is prebaked on a hot platepreferably at a temperature of 60 to 150° C. for 1 to 10 minutes, morepreferably at 80 to 140° C. for 1 to 5 minutes. The resulting resistfilm preferably has a thickness of 0.05 to 2 μm.

Then the resist film is exposed patternwise to excimer laser, EUV or EB.On use of KrF excimer laser, ArF excimer laser or EUV of wavelength 13.5nm, the resist film is exposed through a mask having a desired pattern,preferably in a dose of 1 to 200 mJ/cm², more preferably 10 to 100mJ/cm². On use of EB, a pattern may be written directly or through amask having the desired pattern, preferably in a dose of 1 to 300μC/cm², more preferably 10 to 200 μC/cm².

The exposure may be performed by conventional lithography whereas theimmersion lithography of holding a liquid between the mask and theresist film may be employed if desired. In the immersion lithography,preferably a liquid having a refractive index of at least 1.0 is heldbetween the resist film and the projection lens. The liquid is typicallywater, and in this case, a protective film which is insoluble in watermay be formed on the resist film.

While the water-insoluble protective film which is used in the immersionlithography serves to prevent any components from being leached out ofthe resist film and to improve water sliding on the film surface, it isgenerally divided into two types. The first type is an organicsolvent-strippable protective film which must be stripped, prior toalkaline development, with an organic solvent in which the resist filmis not dissolvable. The second type is an alkali-soluble protective filmwhich is soluble in an alkaline developer so that it can be removedsimultaneously with the removal of solubilized regions of the resistfilm. The protective film of the second type is preferably of a materialcomprising a polymer having a 1,1,1,3,3,3-hexafluoro-2-propanol residue(which is insoluble in water and soluble in an alkaline developer) as abase in an alcohol solvent of at least 4 carbon atoms, an ether solventof 8 to 12 carbon atoms or a mixture thereof. Alternatively, theaforementioned surfactant which is insoluble in water and soluble in analkaline developer may be dissolved in an alcohol solvent of at least 4carbon atoms, an ether solvent of 8 to 12 carbon atoms or a mixturethereof to form a material from which the protective film of the secondtype is formed.

After the exposure, the resist film may be baked (PEB), for example, ona hotplate at 60 to 150° C. for 1 to 5 minutes, preferably at 80 to 140°C. for 1 to 3 minutes.

The resist film is then developed with a developer in the form of anaqueous base solution, for example, 0.1 to 5 wt %, preferably 2 to 3 wt% aqueous solution of tetramethylammonium hydroxide (TMAH) for 0.1 to 3minutes, preferably 0.5 to 2 minutes by conventional techniques such asdip, puddle and spray techniques. In this way, a desired resist patternis formed on the substrate.

Any desired step may be added to the pattern forming process. Forexample, after the resist film is formed, a step of rinsing with purewater (post-soaking) may be introduced to extract the acid generator orthe like from the film surface or wash away particles. After exposure, astep of rinsing (post-soaking) may be introduced to remove any waterremaining on the film after exposure.

Also, a double patterning process may be used for pattern formation. Thedouble patterning process includes a trench process of processing anunderlay to a 1:3 trench pattern by a first step of exposure andetching, shifting the position, and forming a 1:3 trench pattern by asecond step of exposure, for forming a 1:1 pattern; and a line processof processing a first underlay to a 1:3 isolated left pattern by a firststep of exposure and etching, shifting the position, processing a secondunderlay formed below the first underlay by a second step of exposurethrough the 1:3 isolated left pattern, for forming a half-pitch 1:1pattern.

In the pattern forming process, negative tone development may also beused. That is, an organic solvent may be used instead of the aqueousalkaline solution as the developer for developing and dissolving awaythe unexposed region of the resist film.

The organic solvent used as the developer is preferably selected from2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone,2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone,acetophenone, methylacetophenone, propyl acetate, butyl acetate,isobutyl acetate, pentyl acetate, isopentyl acetate, butenyl acetate,propyl formate, butyl formate, isobutyl formate, pentyl formate,isopentyl formate, methyl valerate, methyl pentenoate, methyl crotonate,ethyl crotonate, methyl propionate, ethyl propionate, ethyl3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyllactate, isobutyl lactate, pentyl lactate, isopentyl lactate, methyl2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethylbenzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate. Theseorganic solvents may be used alone or in admixture of two or more.

EXAMPLES

Synthesis Examples, Examples and Comparative Examples are given below byway of illustration and not by way of limitation. The abbreviation “pbw”is parts by weight. For all polymers, Mw and Mn are determined by GPCversus polystyrene standards using THF solvent. THF stands fortetrahydrofuran, and PGMEA for propylene glycol monomethyl etheracetate. Analysis is made by IR spectroscopy, ¹H-NMR spectroscopy, andliquid chromatography-mass spectrometry (LC-MS) using analyticinstruments as shown below.

IR: NICOLET 6700 by Thermo Fisher Scientific Inc.

¹H-NMR: ECA-500 by JEOL Ltd.

LC-MS: Acquity UPLC H-Class system and Acquity QDa by Waters Corp.

[1] Synthesis of Sulfonium Compounds Example 1-1 Synthesis of PAG-1

PAG-1 was synthesized according to the following scheme.

Example 1-1-1 Synthesis of Intermediate 1

In a flask under nitrogen atmosphere, 225 g of Reactant 1, 182 g ofReactant 2, and 4.4 g of copper(I) iodide were dissolved in 700 g ofN-methylpyrrolidone, which was heated at 70° C. Thereafter, 102 g oftriethylamine was added dropwise to the solution, which was aged at 80°C. for 24 hours. After the disappearance of Reactant 1 was confirmed byGC, the reaction system was cooled and 1,000 g of water was addeddropwise to quench the reaction. The reaction solution was extractedwith 2,000 mL of toluene, followed by ordinary aqueous workup, solventdistillation, and recrystallization from hexane. There was obtainedIntermediate 1 as white crystals (amount 233 g, yield 90%).

Example 1-1-2 Synthesis of Intermediate 2

Under nitrogen atmosphere, a flask was charged with 119 g ofIntermediate 1 and 500 g of acetic acid and heated at 30° C. fordissolution. With the temperature kept below 40° C., 41 g of 35 wt %aqueous hydrogen peroxide was added dropwise to the solution. At the endof dropwise addition, the solution was aged at 40° C. for 20 hours.After aging, the reaction system was cooled, a solution of 20 g ofsodium thiosulfate pentahydrate in 400 g of water was added dropwise toquench the reaction. Thereafter, 1,300 mL of toluene and 300 mL of ethylacetate were added to the reaction solution to extract the desiredcompound, followed by ordinary aqueous workup, solvent distillation, andrecrystallization from hexane. There was obtained Intermediate 2 aswhite crystals (amount 115 g, yield 92%).

Example 1-1-3 Synthesis of Intermediate 3

Under nitrogen atmosphere, a flask was charged with 15.6 g ofIntermediate 2, 1.0 g of p-toluenesulfonic acid monohydrate, 15.2 g ofReactant 3, and 70 g of toluene, which were heated under reflux at 105°C. for 7 hours. After the disappearance of Intermediate 2 was confirmedby TLC, the reaction solution was ice cooled and 1.0 g of triethylaminewas added to quench the reaction. Further, 50 mL of saturated aqueoussolution of sodium bicarbonate was added. The desired compound wasextracted with 50 mL of toluene, followed by ordinary aqueous workup,solvent distillation, and purification by silica gel columnchromatography (elute: 15/1 hexane/ethyl acetate). There was obtainedIntermediate 3 as colorless oily matter (amount 21.8 g, yield 98%).

Example 1-1-4 Synthesis of Intermediate 4

In a flask under nitrogen atmosphere, a Grignard reagent was preparedfrom 26.8 g of 4-bromofluorobenzene, 3.7 g of metallic magnesium, and 60g of THF. After the preparation, the flask was cooled, to which asolution of 21.8 g of Intermediate 3 in 25 g of THF was added. Below 20°C., 16.6 g of trimethylsilyl chloride was added dropwise to thesolution, which was aged in an ice bath for 2 hours. At the end ofaging, the reaction system was cooled, and 100 mL of saturated aqueoussolution of ammonium chloride was added dropwise to quench the reaction.This was followed by extraction with 150 mL of methyl isobutyl ketone,ordinary aqueous workup, solvent distillation, and recrystallizationfrom hexane. There was obtained Intermediate 4 as white crystals (amount28.3 g, yield 94%).

Example 1-1-5 Synthesis of Intermediate 5

Under nitrogen atmosphere, 14.2 g of Intermediate 4, 9.0 g ofbenzyltrimethylammonium 1,1-difluoro-2-hydroxyethane-1-sulfonate, 70 gof methyl isobutyl ketone, and 50 g of water were added to a flask.After 30 minutes of stirring, the organic layer was taken out, washedwith water, and concentrated under reduced pressure. The concentrate waswashed with hexane, obtaining Intermediate 5 as oily matter (amount 15.2g, yield 94%).

Example 1-1-6 Synthesis of PAG-1

In nitrogen atmosphere, 0.6 g of sodium hydride was suspended in 56 g ofTHF. After the suspension was cooled below 5° C., a solution of 7.9 g ofIntermediate 5 in 55.5 g of THF was added dropwise thereto. Theresulting solution was aged at room temperature for 12 hours. At the endof aging, the reaction system was cooled and 60 mL of water was addeddropwise to quench the reaction. This was followed by extraction with150 g of methyl isobutyl ketone, ordinary aqueous workup, solventdistillation, and recrystallization from hexane. There was obtainedPAG-1 as white crystals (amount 7.1 g, yield 92%).

PAG-1 was analyzed by IR spectroscopy and LC-MS, with the data shownbelow. FIG. 1 is the ¹H-NMR/DMSO-d₆ spectrum of PAG-1.

IR (D-ATR): v=3484, 3094, 2963, 2872, 1589, 1494, 1397, 1368, 1316,1259, 1237, 1180, 1152, 1110, 1068, 1035, 989, 932, 879, 833, 779, 689,667, 649, 635, 619, 591, 552, 524 cm⁻¹

LC-MS: positive [M+H]⁺ 649

Example 1-2 Synthesis of PAG-2

By following the same procedure as in Example 1-1 aside from usingReactant 4 instead of Reactant 3, PAG-2 was obtained (amount 5.0 g,final step yield 94%).

PAG-2 was analyzed by IR spectroscopy and LC-MS, with the data shownbelow. FIG. 2 is the ¹H-NMR/DMSO-d₆ spectrum of PAG-2.

IR (D-ATR): v=3492, 3064, 2963, 2870, 1589, 1494, 1398, 1365, 1317,1256, 1237, 1215, 1181, 1125, 1104, 1078, 1034, 1009, 988, 949, 914,876, 834, 777, 743, 726, 670, 651, 635, 619, 590, 552, 524 cm⁻¹

LC-MS: positive [M+H]⁺ 607

Example 1-3 Synthesis of PAG-3

By following the same procedure as in Example 1-1 aside from usingReactant 5 instead of Reactant 3, PAG-3 was obtained (amount 4.3 g,final step yield 95%).

PAG-3 was analyzed by LC-MS, with the data shown below.

LC-MS: positive [M+H]⁺ 579

Example 1-4 Synthesis of PAG-4

By following the same procedure as in Example 1-1 aside from usingReactant 6 instead of Reactant 3, PAG-4 was obtained (amount 8.4 g,final step yield 78%).

PAG-4 was analyzed by IR spectroscopy and LC-MS, with the data shownbelow. FIG. 3 is the ¹H-NMR/DMSO-d₆ spectrum of PAG-4.

IR (D-ATR): v=3488, 3096, 2961, 2873, 1589, 1494, 1454, 1399, 1315,1261, 1236, 1172, 1135, 1115, 1073, 1032, 1009, 989, 935, 834, 778, 712,678, 651, 636, 620, 591, 573, 545, 524 cm⁻¹

LC-MS: positive [M+H]⁺ 665

Example 1-5 Synthesis of PAG-5

Example 1-5-1 Synthesis of Intermediate 6

Intermediate 6 was synthesized by the same procedure as in Examples1-1-1 to 1-1-2 aside from using Reactant 7 instead of Reactant 2.

Example 1-5-2 Synthesis of Intermediate 7

Intermediate 7 was synthesized by the same procedure as in Example 1-1-3aside from using Reactant 8 instead of Reactant 3.

Example 1-5-3 Synthesis of PAG-5

PAG-5 was synthesized by the same procedure as in Examples 1-1-4 to1-1-6 aside from using benzyltrimethylammonium1,1,3,3,3-pentafluoro-2-hydroxypropane-1-sulfonate instead ofbenzyltrimethylammonium 1,1-difluoro-2-hydroxyethane-1-sulfonate.

PAG-5 was analyzed by IR spectroscopy and LC-MS, with the data shownbelow. FIG. 4 is the ¹H-NMR/DMSO-d₆ spectrum of PAG-5.

IR (D-ATR): v=3486, 3097, 2976, 1587, 1493, 1448, 1401, 1369, 1318,1245, 1161, 1107, 1087, 1060, 1012, 998, 913, 884, 834, 751, 741, 690,642, 593, 553, 525 cm⁻¹

LC-MS: positive [M+H]⁺ 713

Examples 1-6 to 1-11 Synthesis of PAG-6 to PAG-11

PAG-6 to PAG-11 were synthesized by any well-known organic chemistrymethods using corresponding reactants.

[2] Synthesis of Base Resins

Base resins (or polymers) used in resist compositions were synthesizedby the following procedure.

Synthesis Example 1 Synthesis of Polymer P-1

In a funnel under nitrogen atmosphere, 5.0 g of 3-hydroxy-1-adamantylmethacrylate, 14.4 g of α-methacryloxy-γ-butyrolactone, 20.8 g of1-isopropylcyclopentyl methacrylate, 0.49 g of dimethyl2,2′-azobis(2-methylpropionate) (V-601 by Wako Pure Chemical Industries,Ltd.), 0.41 g of 2-mercaptoethanol, and 56 g of PGMEA were combined toform a monomer/initiator solution. A flask in nitrogen atmosphere wascharged with 19 g of PGMEA, which was heated at 80° C. with stirring.With stirring, the monomer/initiator solution was added dropwise to theflask over 4 hours. After the completion of dropwise addition, thepolymerization solution was continuously stirred for 2 hours whilemaintaining the temperature of 80° C. The polymerization solution wascooled to room temperature, whereupon it was added dropwise to 640 g ofmethanol with vigorous stirring. The precipitate was collected byfiltration, washed twice with 240 g of methanol, and vacuum dried at 50°C. for 20 hours, obtaining Polymer P-1 in white powder form (amount 35.3g, yield 88%). On GPC analysis, Polymer P-1 had a Mw of 8,500 and aMw/Mn of 1.58.

Synthesis Examples 2 to 6 Synthesis of Polymers P-2 to P-6

Polymers P-2 to P-6 were synthesized by the same procedure as inSynthesis Example 1 aside from changing the type and amount of monomers.

[3] Preparation of Resist Composition Examples 2-1 to 2-44 andComparative Examples 1-1 to 1-18

Chemically amplified resist compositions in solution form were preparedby dissolving a sulfonium compound (PAG-1 to PAG-11) or comparativephotoacid generator (PAG-A to PAG-E), base resin (Polymers P-1 to P-6),other photoacid generator (PAG-X, PAG-Y), quencher (Q-1 to Q-4), andalkali-soluble surfactant (SF-1) in a solvent containing 0.01 wt % ofsurfactant A in accordance with the formulation shown in Tables 1 to 3,and filtering through a Teflon® filter with a pore size of 0.2 μm.

TABLE 1 Other Photoacid photoacid Resist Base resin generator generatorQuencher Surfactant Solvent 1 Solvent 2 composition (pbw) (pbw) (pbw)(pbw) (pbw) (pbw) (pbw) Example 2-1 R-01 P-1 PAG-1 PAG-X Q-1 SF-1 PGMEAGBL (80) (4.0) (5.0) (7.0) (3.0) (1,728) (192) 2-2 R-02 P-1 PAG-2 PAG-XQ-1 SF-1 PGMEA GBL (80) (4.0) (5.0) (7.0) (3.0) (1,728) (192) 2-3 R-03P-1 PAG-3 PAG-X Q-1 SF-1 PGMEA GBL (80) (4.0) (5.0) (7.0) (3.0) (1,728)(192) 2-4 R-04 P-1 PAG-4 PAG-X Q-1 SF-1 PGMEA GBL (80) (4.0) (5.0) (7.0)(3.0) (1,728) (192) 2-5 R-05 P-1 PAG-6 PAG-X Q-1 SF-1 PGMEA GBL (80)(4.0) (5.0) (7.0) (3.0) (1,728) (192) 2-6 R-06 P-1 PAG-7 PAG-X Q-1 SF-1PGMEA GBL (80) (4.0) (5.0) (7.0) (3.0) (1,728) (192) 2-7 R-07 P-1 PAG-8PAG-X Q-1 SF-1 PGMEA GBL (80) (4.0) (5.0) (7.0) (3.0) (1,728) (192) 2-8R-08 P-1 PAG-10 PAG-X Q-1 SF-1 PGMEA GBL (80) (4.0) (5.0) (7.0) (3.0)(1,728) (192) 2-9 R-09 P-1 PAG-11 PAG-X Q-1 SF-1 PGMEA GBL (80) (4.0)(5.0) (7.0) (3.0) (1,728) (192) 2-10 R-10 P-2 PAG-1 PAG-X Q-1 SF-1 PGMEAGBL (80) (4.5) (5.0) (3.5) (3.0) (1,728) (192) 2-11 R-11 P-2 PAG-2 PAG-XQ-1 SF-1 PGMEA GBL (80) (4.0) (4.5) (3.5) (3.0) (1,728) (192) 2-12 R-12P-2 PAG-4 PAG-Y Q-1 SF-1 PGMEA GBL (80) (3.5) (5.0) (4.5) (3.0) (1,728)(192) 2-13 R-13 P-2 PAG-5 PAG-X Q-2 SF-1 PGMEA GBL (80) (4.0) (5.5)(4.5) (3.0) (1,728) (192) 2-14 R-14 P-2 PAG-6 PAG-X Q-1 SF-1 PGMEA GBL(80) (4.0) (4.5) (3.5) (3.0) (1,728) (192) 2-15 R-15 P-2 PAG-9 PAG-X Q-1SF-1 PGMEA GBL (80) (4.0) (5.5) (3.5) (3.0) (1,728) (192) 2-16 R-16 P-2PAG-10 PAG-Y Q-4 SF-1 PGMEA GBL (80) (4.0) (4.5) (3.5) (3.0) (1,728)(192) 2-17 R-17 P-2 PAG-11 PAG-Y Q-3 SF-1 PGMEA GBL (80) (3.0) (4.0)(3.0) (3.0) (1,728) (192) 2-18 R-18 P-3 PAG-1 PAG-Y Q-1 SF-1 PGMEA GBL(80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 2-19 R-19 P-3 PAG-2 PAG-Y Q-1SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 2-20 R-20 P-3PAG-3 PAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728)(192) 2-21 R-21 P-3 PAG-4 PAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0) (8.0)(2.5) (3.0) (1,728) (192) 2-22 R-22 P-3 PAG-5 PAG-Y Q-1 SF-1 PGMEA GBL(80) (5.0) (8.0) (2.5) (3.0) (1,728) (192)

TABLE 2 Other Photoacid photoacid Resist Base resin generator generatorQuencher Surfactant Solvent 1 Solvent 2 composition (pbw) (pbw) (pbw)(pbw) (pbw) (pbw) (pbw) Example 2-23 R-23 P-3 PAG-6 PAG-Y Q-1 SF-1 PGMEAGBL (80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 2-24 R-24 P-3 PAG-7 PAG-YQ-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 2-25 R-25P-3 PAG-8 PAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728)(192) 2-26 R-26 P-3 PAG-9 PAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0) (8.0)(2.5) (3.0) (1,728) (192) 2-27 R-27 P-3 PAG-10 PAG-Y Q-1 SF-1 PGMEA GBL(80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 2-28 R-28 P-3 PAG-11 PAG-YQ-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 2-29 R-29P-4 PAG-1 PAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728)(192) 2-30 R-30 P-4 PAG-2 PAG-Y Q-1 SF-1 PGMEA GBL (80) (4.5) (8.5)(3.5) (3.0) (1,728) (192) 2-31 R-31 P-4 PAG-4 PAG-X Q-3 SF-1 PGMEA GBL(80) (5.0) (5.5) (3.0) (3.0) (1,728) (192) 2-32 R-32 P-4 PAG-5 PAG-X Q-1SF-1 PGMEA GBL (80) (5.5) (6.5) (3.5) (3.0) (1,728) (192) 2-33 R-33 P-4PAG-7 PAG-Y Q-1 SF-1 PGMEA GBL (80) (4.5) (7.0) (3.5) (3.0) (1,728)(192) 2-34 R-34 P-4 PAG-9 PAG-Y Q-3 SF-1 PGMEA GBL (80) (5.0) (8.0)(4.0) (3.0) (1,728) (192) 2-35 R-35 P-4 PAG-10 PAG-Y Q-2 SF-1 PGMEA GBL(80) (5.0) (7.5) (4.5) (3.0) (1,728) (192) 2-36 R-36 P-4 PAG-11 PAG-XQ-4 SF-1 PGMEA GBL (80) (3.0) (6.5) (3.0) (3.0) (1,728) (192) 2-37 R-37P-5 PAG-1 — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5) (3.0) (1,728) (192) 2-38R-38 P-5 PAG-7 — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5) (3.0) (1,728) (192)2-39 R-39 P-5 PAG-11 — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5) (3.0) (1,728)(192) 2-40 R-40 P-6 PAG-1 PAG-Y Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5)(3.5) (3.0) (1,728) (192) 2-41 R-41 P-6 PAG-1 — Q-1 SF-1 PGMEA DAA (80)(3.0) (3.5) (3.0) (1,728) (192) 2-42 R-42 P-6 PAG-7 — Q-1 SF-1 PGMEA DAA(80) (3.0) (3.5) (3.0) (1,728) (192) 2-43 R-43 P-6 PAG-11 — Q-1 SF-1PGMEA DAA (80) (3.0) (3.5) (3.0) (1,728) (192) 2-44 R-44 P-1 PAG-1 PAG-YQ-1 SF-1 PGMEA DAA (80) (3.0) (2.0) (3.5) (3.0) (1,728) (192)

TABLE 3 Other Photoacid photoacid Resist Base resin generator generatorQuencher Surfactant Solvent 1 Solvent 2 composition (pbw) (pbw) (pbw)(pbw) (pbw) (pbw) (pbw) Comparative 1-1 R-45 P-1 PAG-A PAG-X Q-1 SF-1PGMEA GBL Example (80) (4.0) (5.0) (7.0) (3.0) (1,728) (192) 1-2 R-46P-1 PAG-B PAG-X Q-1 SF-1 PGMEA GBL (80) (4.0) (5.0) (7.0) (3.0) (1,728)(192) 1-3 R-47 P-1 PAG-C PAG-X Q-1 SF-1 PGMEA GBL (80) (4.0) (5.0) (7.0)(3.0) (1,728) (192) 1-4 R-48 P-1 PAG-D PAG-X Q-1 SF-1 PGMEA GBL (80)(4.0) (5.0) (7.0) (3.0) (1,728) (192) 1-5 R-49 P-1 PAG-E PAG-X Q-1 SF-1PGMEA GBL (80) (4.0) (5.0) (7.0) (3.0) (1,728) (192) 1-6 R-50 P-3 PAG-APAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 1-7R-51 P-3 PAG-B PAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0)(1,728) (192) 1-8 R-52 P-3 PAG-C PAG-Y Q-1 SF-1 PGMEA GBL (80) (5.0)(8.0) (2.5) (3.0) (1,728) (192) 1-9 R-53 P-3 PAG-D PAG-Y Q-1 SF-1 PGMEAGBL (80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 1-10 R-54 P-3 PAG-E PAG-YQ-1 SF-1 PGMEA GBL (80) (5.0) (8.0) (2.5) (3.0) (1,728) (192) 1-11 R-55P-5 PAG-B — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5) (3.0) (1,728) (192) 1-12R-56 P-5 PAG-C — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5) (3.0) (1,728) (192)1-13 R-57 P-5 PAG-D — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5) (3.0) (1,728)(192) 1-14 R-58 P-5 — — Q-1 SF-1 PGMEA DAA (80) (3.5) (3.0) (1,728)(192) 1-15 R-59 P-6 PAG-B — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5) (3.0)(1,728) (192) 1-16 R-60 P-6 PAG-C — Q-1 SF-1 PGMEA DAA (80) (3.0) (3.5)(3.0) (1,728) (192) 1-17 R-61 P-6 PAG-D — Q-1 SF-1 PGMEA DAA (80) (3.0)(3.5) (3.0) (1,728) (192) 1-18 R-62 P-6 — — Q-1 SF-1 PGMEA DAA (80)(3.5) (3.0) (1,728) (192)

The solvents, other photoacid generators PAG-X to PAG-Z, comparativephotoacid generators PAG-A to PAG-E, and quenchers Q-1 to Q-4,alkali-soluble surfactant SF-1, and surfactant A in Tables 1 to 3 areidentified below.

Solvent:

PGMEA (propylene glycol monomethyl ether acetate)

GBL (γ-butyrolactone)

DAA (diacetone alcohol)

Other Photoacid Generator: PAG-X and PAG-Y

Comparative Photoacid Generator: PAG-A to PAG-E

Quencher: Q-1 to Q-4

Alkali-Soluble Surfactant SF-1:

poly(2,2,3,3,4,4,4-heptafluoro-1-isobutyl-1-butylmethacrylate/9-(2,2,2-trifluoro-1-trifluoroethyloxycarbonyl)-4-oxatricyclo[4.2.1.0^(3,7)]nonan-5-on-2-ylmethacrylate)

Mw=7,700

Mw/Mn=1.82

Surfactant A3-methyl-3-(2,2,2-trifluoroethoxymethyl)oxetane/tetrahydrofuran/2,2-dimethyl-1,3-propanediol copolymer (Omnova Solutions, Inc.)

a:(b+b′):(c+c′)=1:4-7:0.01-1 (molar ratio)

Mw=1,500

[4] Evaluation of Resist Composition: ArF Lithography Patterning Test 1Examples 3-1 to 3-17 and Comparative Examples 2-1 to 2-5

On a silicon substrate, an antireflective coating solution (ARC29A,Nissan Chemical Corp.) was coated and baked at 200° C. for 60 seconds toform an ARC of 100 nm thick. Each of the resist compositions (R-01 toR-17, R-45 to R-49) was spin coated on the ARC and prebaked on ahotplate at 100° C. for 60 seconds to form a resist film of 90 nm thickon the ARC. The wafer was exposed on an ArF excimer laser immersionlithography scanner (NSR-S610C by Nikon Corp., NA 1.30, dipoleillumination) through a Cr mask having a line-and-space (L/S) patternwith a line width of 40 nm and a pitch of 80 nm (on-wafer size), whilevarying the exposure dose and focus at a dose pitch of 1 mJ/cm² and afocus pitch of 0.025 μm. The immersion liquid used herein was water.After exposure, the resist film was baked (PEB) at the temperature shownin Table 4 for 60 seconds. The resist film was puddle developed in a2.38 wt % tetramethylammonium hydroxide (TMAH) aqueous solution for 30seconds, rinsed with deionized water and spin dried, forming a positivepattern. The L/S pattern after development was observed under CD-SEM(CG4000 by Hitachi High-Technologies Corp.), whereupon sensitivity, EL,MEF, LWR, and defect density were evaluated by the following methods.The results are shown in Table 4.

Evaluation of Sensitivity

The optimum exposure dose Eop (mJ/cm²) which provided a L/S patternhaving a line width of 40 nm and a pitch of 80 nm was determined as anindex of sensitivity. A smaller dose value indicates a highersensitivity.

Evaluation of Exposure Latitude (EL)

The exposure dose which provided a L/S pattern with a space width of 40nm±10% (i.e., 36 nm to 44 nm) was determined. EL (%) is calculated fromthe exposure doses according to the following equation:EL(%)=(|E1−E2|/Eop)×100wherein E1 is an optimum exposure dose which provides a L/S pattern witha line width of 36 nm and a pitch of 80 nm, E2 is an optimum exposuredose which provides a L/S pattern with a line width of 44 nm and a pitchof 80 nm, and Eop is an optimum exposure dose which provides a L/Spattern with a line width of 40 nm and a pitch of 80 nm.Evaluation of Mask Error Factor (MEF)

A L/S pattern was formed by exposure in the optimum dose Eop through themask with the pitch fixed and the line width varied. MEF was calculatedfrom the mask line width and a variation of the pattern line widthaccording to the following equation:MEF=(pattern line width)/(mask line width)−bwherein b is a constant. A value closer to unity (1) indicates betterperformance.Evaluation of Line Width Roughness (LWR)

A L/S pattern was formed by exposure in the optimum dose Eop. The linewidth was measured at longitudinally spaced apart 10 points, from whicha 3-fold value (3σ) of standard deviation (σ) was determined andreported as LWR. A smaller value of 3σ indicates a pattern having alower roughness and more uniform line width.

Evaluation of Defect Density

Defects in the pattern as developed were inspected by a flaw detectorKLA2800 (KLA-Tencor). A defect density (count/cm²) was computed bydividing the total number of detected defects by a detection area. Thepattern formed was an iterated 50-nm 1:1 L/S pattern. The defectinspection conditions included light source UV, inspected pixel size0.28 μm, and cell-to-cell mode. In this test, the sample was rated goodfor a defect density of less than 0.05 defect/cm² and poor for a densityof equal to or more than 0.05 defect/cm².

TABLE 4 Resist PEB temp. Eop EL LWR Defect composition (° C.) (mJ/cm²)(%) MEF (nm) density Example 3-1 R-01 90 35 17.5 2.5 2.6 good 3-2 R-0290 38 18.0 2.4 2.4 good 3-3 R-03 90 36 16.5 2.2 2.3 good 3-4 R-04 90 3413.5 2.8 2.9 good 3-5 R-05 90 35 18.5 2.6 2.2 good 3-6 R-06 90 34 14.32.7 2.5 good 3-7 R-07 90 35 17.5 2.5 2.7 good 3-8 R-08 90 39 19.2 2.12.3 good 3-9 R-09 95 38 19.1 1.9 2.3 good 3-10 R-10 95 35 18.5 2.4 2.4good 3-11 R-11 95 36 17.3 2.3 2.3 good 3-12 R-12 95 33 14.1 2.9 2.8 good3-13 R-13 95 36 13.8 2.8 2.9 good 3-14 R-14 95 38 19.7 2.4 2.1 good 3-15R-15 95 36 15.6 2.3 2.6 good 3-16 R-16 95 39 16.9 1.9 2.5 good 3-17 R-1795 38 17.4 2.0 2.3 good Comparative 2-1 R-45 90 32 9.1 3.3 4.2 poorExample 2-2 R-46 90 33 11.2 3.2 4.0 poor 2-3 R-47 90 30 10.8 3.9 3.9poor 2-4 R-48 90 29 8.9 3.8 4.0 poor 2-5 R-49 90 29 8 3.3 4.1 poor

As is evident from Table 4, the chemically amplified resist compositionscontaining sulfonium compounds within the scope of the invention exhibita satisfactory sensitivity, improved values of EL, MEF and LWR and areeffective in reducing development defects. The resist compositions areuseful as the ArF immersion lithography material.

[5] Evaluation of Resist Composition: ArF Lithography Patterning Test 2Examples 4-1 to 4-19 and Comparative Examples 3-1 to 3-5

On a substrate, a spin-on carbon film ODL-180 (Shin-Etsu Chemical Co.,Ltd.) having a carbon content of 80 wt % was deposited to a thickness of180 nm and a silicon-containing spin-on hard mask SHB-A941 having asilicon content of 43 wt % was deposited thereon to a thickness of 35nm. On this substrate for trilayer process, each of the resistcompositions (R-18 to R-36, R-50 to R-54) was spin coated, then baked ona hot plate at 100° C. for 60 seconds to form a resist film of 100 nmthick.

Using an ArF excimer laser immersion lithography scanner NSR-S610C(Nikon Corp., NA 1.30, σ 0.90/0.72, cross-pole opening 35 deg.,cross-pole illumination, azimuthally polarized illumination), exposurewas performed through a 6% halftone phase shift mask bearing a contacthole (CH) pattern with a hole size of 45 nm and a pitch of 110 nm(on-wafer size) while varying the dose and focus (dose pitch: 1 mJ/cm²,focus pitch: 0.025 μm). The immersion liquid used herein was water.After the exposure, the wafer was baked (PEB) at the temperature shownin Table 5 for 60 seconds. Thereafter, the resist film was puddledeveloped in n-butyl acetate for 30 seconds, rinsed with4-methyl-2-pentanol, and spin dried, obtaining a negative pattern. TheCH pattern after development was observed under CD-SEM CG4000 (HitachiHigh Technologies Corp.) whereupon sensitivity, MEF, CDU, and DOF wereevaluated by the following methods. The results are shown in Table 5.

Evaluation of Sensitivity

The optimum dose Eop (mJ/cm²) which provided a CH pattern with a holesize of 45 nm and a pitch of 110 nm was determined as an index ofsensitivity. A smaller dose value indicates a higher sensitivity.

Evaluation of MEF

A CH pattern was formed by exposure at the optimum dose Eop by ArFlithography patterning test 2 with the pitch fixed and the mask sizevaried. MEF was calculated from the mask size and a variation of the CHpattern size according to the following equation:MEF=(pattern size)/(mask size)−bwherein b is a constant. A value closer to unity (1) indicates betterperformance.Evaluation of Critical Dimension Uniformity (CDU)

For the CH pattern formed by exposure at the optimum dose Eop, the holesize was measured at 10 areas subject to an identical dose of shot (9contact holes per area), from which a 3-fold value (3σ) of standarddeviation (σ) was determined and reported as CDU. A smaller value of 3σindicates a CH pattern having improved CDU.

Evaluation of Depth of Focus (DOF)

As an index of DOF, a range of focus which provided a CH pattern with asize of 45 nm±10% (i.e., 41 to 49 nm) was determined. A greater valueindicates a wider DOF.

Evaluation of Film Retention

The CH pattern printed from exposure at Eop was observed in crosssection under CD-SEM (S-4800 by Hitachi High-Technologies Corp.). Thefilm thickness as developed divided by the film thickness 100 nm as spincoated is reported as an index of film retention. A greater valueindicates better film retention.

TABLE 5 Film Resist PEB temp. Eop CDU DOF retention composition (° C.)(mJ/cm²) MEF (nm) (nm) (%) Example 4-1 R-18 95 35 2.3 3.1 150 71 4-2R-19 95 36 2.5 2.9 140 75 4-3 R-20 95 34 2.2 3.3 150 68 4-4 R-21 95 382.7 3.5 130 65 4-5 R-22 95 40 2.8 3.4 120 70 4-6 R-23 95 38 2.4 3.0 15070 4-7 R-24 95 39 2.7 3.4 110 72 4-8 R-25 95 35 2.2 3.1 140 70 4-9 R-2695 38 2.4 3.1 130 69 4-10 R-27 95 38 2.3 3.3 150 73 4-11 R-28 95 39 2.42.8 160 70 4-12 R-29 85 41 2.5 2.9 130 68 4-13 R-30 85 42 2.1 3.1 140 694-14 R-31 85 41 2.8 3.6 120 68 4-15 R-32 85 45 2.8 3.5 130 72 4-16 R-3385 44 2.9 3.7 120 70 4-17 R-34 85 43 2.4 3.1 150 70 4-18 R-35 85 42 2.43.3 140 72 4-19 R-36 85 42 2.3 3.2 150 71 Comparative 3-1 R-50 85 38 2.54.0 80 60 Example 3-2 R-51 85 37 3.0 4.1 90 59 3-3 R-52 85 35 2.9 3.8 7063 3-4 R-53 85 38 3.3 3.9 80 62 3-5 R-54 85 41 3.4 4.2 90 63

As is evident from Table 5, the chemically amplified resist compositionscontaining sulfonium compounds within the scope of the invention exhibita satisfactory sensitivity and improved values of CDU, MEF and DOF informing negative patterns via organic solvent development. Satisfactoryfilm retention is also confirmed. The resist compositions are alsouseful in the organic solvent development process.

[6] Evaluation of Resist Composition: EB Lithography Test Examples 5-1to 5-8 and Comparative Examples 4-1 to 4-8

An antireflective coating solution (DUV-42, Nissan Chemical Corp.) wascoated on a silicon substrate and baked at 200° C. for 60 seconds toform an ARC of 61 nm thick. Each of the resist compositions (R-37 toR-44, R-55 to R-62) was spin coated on the ARC and prebaked on ahotplate at 100° C. for 60 seconds to form a resist film of 45 nm thick.Using an EB lithography system ELS-F125 (Elionix Co., Ltd., acceleratingvoltage 125 kV), the resist film was exposed to EB through a maskbearing a CH pattern with a hole size of 24 nm and a pitch of 48 nm(on-wafer size) while varying the dose from 50 μC/cm² at a step of 5μC/cm². The resist film was baked (PEB) at the temperature shown inTable 6 for 60 seconds. The resist film was then puddle developed in a2.38 wt % TMAH aqueous solution for 30 seconds, rinsed with deionizedwater, and spin dried, yielding a positive resist pattern. The CHpattern after development was observed under CD-SEM S9380 (Hitachi HighTechnologies Corp.) whereupon sensitivity, EL, and CDU were evaluated bythe following methods. The results are shown in Table 6.

Evaluation of Sensitivity

The optimum dose Eop (μC/cm²) which provided a CH pattern with a holesize of 24 nm and a pitch of 48 nm was determined as an index ofsensitivity. A smaller dose value indicates a higher sensitivity.

Evaluation of EL

The exposure dose which provided a CH pattern with a hole size of 24nm±10% (i.e., 21.6 nm to 26.4 nm) was determined. EL (%) is calculatedfrom the exposure doses according to the following equation:EL(%)=(|E1−E2|/Eop)×100wherein E1 is an optimum exposure dose which provides a CH pattern witha hole size of 21.6 nm and a pitch of 48 nm, E2 is an optimum exposuredose which provides a CH pattern with a hole size of 26.4 nm and a pitchof 48 nm, and Eop is an optimum exposure dose which provides a CHpattern with a hole size of 24 nm and a pitch of 48 nm.Evaluation of CDU

For the CH pattern formed by exposure at the optimum dose Eop, the holesize was measured at 10 areas subject to an identical dose of shot (9contact holes per area), from which a 3-fold value (3σ) of standarddeviation (σ) was determined and reported as CDU. A smaller value of 3σindicates a CH pattern having improved CDU.

TABLE 6 Resist PEB temp. Eop EL CDU composition (° C.) (μC/cm²) (%) (nm)Example 5-1 R-37 105 153 13.5 3.3 5-2 R-38 105 158 12.3 3.6 5-3 R-39 105160 15.6 3.2 5-4 R-40 105 155 16.3 3.1 5-5 R-41 105 157 15.8 3.5 5-6R-42 105 160 15.3 3.3 5-7 R-43 105 154 13.2 3.1 5-8 R-44 105 155 15.33.4 Comparative 4-1 R-55 105 130 9.0 4.2 Example 4-2 R-56 105 135 10.13.9 4-3 R-57 105 145 8.8 4.3 4-4 R-58 105 144 9.5 3.8 4-5 R-59 105 15110.2 4.1 4-6 R-60 105 133 9.8 4.0 4-7 R-61 105 142 8.3 4.2 4-8 R-62 105120 9.6 4.5

It is evident from Table 6 that the chemically amplified resistcompositions containing sulfonium compounds within the scope of theinvention exhibit a high sensitivity, improved EL and CDU. The resistcompositions are useful EB and EUV lithography materials.

Japanese Patent Application No. 2019-072757 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A sulfonium compound having the formula(A):

wherein Q¹ and Q² are each independently fluorine or a C₁-C₆ fluoroalkylgroup, Q³ and Q⁴ are each independently hydrogen, fluorine or a C₁-C₆fluoroalkyl group, a is an integer of 1 to 4, b is 1 or 2, c is aninteger of 0 to 3, L^(a1) to L^(a4) are each independently a singlebond, ether bond, ester bond, sulfonic acid ester bond, carbonate bondor carbamate bond, X^(L1) and X^(L2) are each independently a singlebond or a C₂-C₄₀ divalent hydrocarbon group which may contain aheteroatom, R^(a) is hydrogen or a C₁-C₂₀ monovalent hydrocarbon groupwhich may contain a heteroatom, R^(b) and R^(c) are each independently aC₂-C₄₀ monovalent hydrocarbon group which may contain a heteroatom,R^(b) and R^(c) may bond together to form a ring with the oxygen atomsto which they are attached and the intervening carbon atom, R¹ is aC₁-C₅₀ (a+1)-valent hydrocarbon group which may contain a heteroatom, R²is a C₁-C₅₀ monovalent hydrocarbon group which may contain a heteroatom,R³ is a C₁-C₅₀ divalent hydrocarbon group which may contain aheteroatom, in the case of b=1, R¹ and R², or R² and R³ may bondtogether to form a ring with the sulfur atom to which they are attached,and in the case of b=2, R¹ and R³, or two R¹ may bond together to form aring with the sulfur atom to which they are attached.
 2. The sulfoniumcompound of claim 1, having the formula (A-1):

wherein Q¹ to Q⁴, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a), R^(b), R^(c),R², R³, a, b and c are as defined above R^(d) is a C₁-C₂₀ monovalenthydrocarbon group which may contain a heteroatom, d is an integer of 0to 4, the sum a+d is 1 to 5, in the case of d≥2, each R^(d) may be thesame or different, and two R^(d) may bond together to form a ring withthe atoms to which they are attached.
 3. The sulfonium compound of claim2, having the formula (A-2):

wherein Q¹ to Q⁴, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a) to R^(d), a,b, c and d are as defined above, R^(e) and R^(f) are each independentlya C₁-C₂₀ monovalent hydrocarbon group which may contain a heteroatom, eis an integer of 0 to 5, f is an integer of 0 to 4, in the case of e≥2,each R^(e) may be the same or different, and two R^(e) may bond togetherto form a ring with the atoms to which they are attached, and in thecase of f≥2, each R^(f) may be the same or different, and two R^(f) maybond together to form a ring with the atoms to which they are attached.4. The sulfonium compound of claim 3, having the formula (A-3):

wherein Q¹ to Q³, L^(a1) to L^(a4), X^(L1), X^(L2), R^(a) to R^(f), a,b, d, e and f are as defined above.
 5. A photoacid generator comprisingthe sulfonium compound of claim
 1. 6. A chemically amplified resistcomposition comprising the photoacid generator of claim 5 and a baseresin comprising recurring units having the formula (a1) or (a2):

wherein R^(A) is each independently hydrogen, fluorine, methyl ortrifluoromethyl, Z^(A) is a single bond, phenylene, naphthylene or(backbone)-C(═O)—O—Z^(A1)—, Z^(A1) is a C₁-C₁₀ alkanediyl group whichmay contain a hydroxyl moiety, ether bond, ester bond or lactone ring,or phenylene or naphthylene, Z^(B) is a single bond or(backbone)-C(═O)—O—, X^(A) and X^(B) are each independently an acidlabile group, R¹¹ is a C₁-C₂₀ monovalent hydrocarbon group which maycontain a heteroatom, and n is an integer of 0 to
 4. 7. The resistcomposition of claim 6 wherein the base resin further comprisesrecurring units having the formula (b1) or (b2):

wherein R^(A) is each independently hydrogen, fluorine, methyl ortrifluoromethyl, Y^(A) is hydrogen or a polar group containing at leastone structure selected from the group consisting of hydroxyl, cyano,carbonyl, carboxyl, ether bond, ester bond, sulfonic acid ester bond,carbonate bond, lactone ring, sultone ring and carboxylic anhydride, andm is 1 or
 2. 8. The resist composition of claim 6 wherein the base resinfurther comprises recurring units of at least one type selected fromrecurring units having the formulae (c1) to (c3):

wherein R^(A) is each independently hydrogen, fluorine, methyl ortrifluoromethyl, Z¹ is a single bond, phenylene, —O—Z¹¹—, —C(═O)—O—Z¹¹—or —C(═O)—NH—Z¹¹—, Z¹¹ is a C₁-C₂₀ alkanediyl group, C₂-C₂₀ alkenediylgroup or phenylene group, which may contain a carbonyl moiety, esterbond, ether bond or hydroxyl moiety, Z² is a single bond or—Z²¹—C(═O)—O—, Z²¹ is a C₁-C₂₀ divalent hydrocarbon group which maycontain a heteroatom, Z³ is a single bond, methylene, ethylene,phenylene, fluorinated phenylene, —O—Z³¹—, —C(═O)—O—Z³¹— or—C(═O)—NH—Z³¹—, Z³¹ is a C₁-C₆ alkanediyl group, C₂-C₆ alkenediyl groupor phenylene group, which may contain a carbonyl moiety, ester bond,ether bond or hydroxyl moiety, R²¹ and R²² are each independently aC₁-C₂₀ monovalent hydrocarbon group which may contain a heteroatom, R²¹and R²² may bond together to form a ring with the sulfur atom to whichthey are attached, M⁻ is a non-nucleophilic counter ion, and A⁺ is anammonium, sulfonium or iodonium cation.
 9. The resist composition ofclaim 6, further comprising an organic solvent.
 10. The resistcomposition of claim 6, further comprising another photoacid generatorother than the photoacid generator.
 11. The resist composition of claim10 wherein the other photoacid generator has the formula (1) or (2):

wherein R¹⁰¹, R¹⁰² and R¹⁰³ are each independently a C₁-C₂₀ monovalenthydrocarbon group which may contain a heteroatom, any two of R¹⁰¹, R¹⁰²and R¹⁰³ may bond together to form a ring with the sulfur atom to whichthey are attached, and X⁻ is an anion selected from the followingformulae (1A) to (1D):

wherein R^(fa), R^(fb1), R^(fb2), R^(fc1), R^(fc2) and R^(fc3) are eachindependently fluorine or a C₁-C₄₀ monovalent hydrocarbon group whichmay contain a heteroatom, or a pair of R^(fb1) and R^(fb2), or R^(fc1)and R^(fc2) may bond together to form a ring with the carbon atom towhich they are attached and any intervening atoms, R^(fd) is a C₁-C₄₀monovalent hydrocarbon group which may contain a heteroatom,

wherein R²⁰¹ and R²⁰² are each independently a C₁-C₃₀ monovalenthydrocarbon group which may contain a heteroatom, R²⁰³ is a C₁-C₃₀divalent hydrocarbon group which may contain a heteroatom, any two ofR²⁰¹, R²⁰² and R²⁰³ may bond together to form a ring with the sulfuratom to which they are attached, L^(A) is a single bond, ether bond or aC₁-C₂₀ divalent hydrocarbon group which may contain a heteroatom, X^(a),X^(b), X^(c) and X^(d) are each independently hydrogen, fluorine ortrifluoromethyl, at least one of X^(a), X^(b), X^(c) and X^(d) beingfluorine or trifluoromethyl.
 12. The resist composition of claim 6,further comprising a compound having the formula (3) or (4):R^(q1)—SO₃ ⁻Mq⁺  (3)R^(q2)—CO₂ ⁻Mq⁺  (4) wherein R^(q1) is hydrogen or a C₁-C₄₀ monovalenthydrocarbon group which may contain a heteroatom, exclusive of the groupwherein hydrogen bonded to the carbon atom at α-position relative to thesulfo group is substituted by fluorine or fluoroalkyl, R^(q2) ishydrogen or a C₁-C₄₀ monovalent hydrocarbon group which may contain aheteroatom, and Mq⁺ is an onium cation.
 13. The resist composition ofclaim 6, further comprising an amine compound.
 14. The resistcomposition of claim 6, further comprising a surfactant which isinsoluble or substantially insoluble in water and soluble in alkalinedeveloper, and/or a surfactant which is insoluble or substantiallyinsoluble in water and alkaline developer.
 15. A pattern forming processcomprising the steps of applying the chemically amplified resistcomposition of claim 6 to form a resist film on a substrate, exposing aselected region of the resist film to KrF excimer laser, ArF excimerlaser, EB or EUV, and developing the exposed resist film in a developer.16. The pattern forming process of claim 15 wherein the developing stepuses an alkaline aqueous solution as the developer, thereby forming apositive pattern in which an exposed region of the resist film isdissolved away and an unexposed region of the resist film is notdissolved.
 17. The pattern forming process of claim 15 wherein thedeveloping step uses an organic solvent as the developer, therebyforming a negative pattern in which an unexposed region of the resistfilm is dissolved away and an exposed region of the resist film is notdissolved.
 18. The pattern forming process of claim 17 wherein theorganic solvent is at least one solvent selected from the groupconsisting of 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate,isopentyl acetate, propyl formate, butyl formate, isobutyl formate,pentyl formate, isopentyl formate, methyl valerate, methyl pentenoate,methyl crotonate, ethyl crotonate, methyl propionate, ethyl propionate,ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate,butyl lactate, isobutyl lactate, pentyl lactate, isopentyl lactate,methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methylphenylacetate, benzyl formate, phenylethyl formate, methyl3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and2-phenylethyl acetate.
 19. The process of claim 15 wherein the exposurestep is carried out by immersion lithography while a liquid having arefractive index of at least 1.0 is held between the resist film and aprojection lens.
 20. The process of claim 19, further comprising thestep of forming a protective film on the resist film prior to theexposure step, wherein immersion lithography is carried out while theliquid is held between the protective film and the projection lens.